Not sure why. I would speculate maybe the designers thought that with limited keys - you can't cover bass clef and treble clef fully - so the bias is toward the "lead" and treble clef is provided more fully by default.

Regardless of the "why" - check out a previous answer from Yamaha support on the same subject:

https://www.yamahasynth.com/ask-a-question/mx61-starts-1-octave

Although this covers the 61 (and yes, it is biased the same as the MX49) - the answer still applies equally for the MX49.

Hi Jason,
I posted the same question on FB MX group and consensus is the same. Most people suppose Yamaha preferred the lead higher octaves for their shorter keyboards. However why is a mystery. 🙂 Less important but also interesting is that Yamaha calls middle-C a C3 while in general it is called C4. It has supposedly to do with some specific octave count that Yamaha uses...?

Middle “C” as C3 or C4 is a convention. All that is necessary is that you know which convention is being used by the manufacturer of the instrument. Either is fine. In parts of the world Celsius is the temperature convention, in other parts of the world it’s Fahrenheit — as long as you know which convention is being used, you’ll be fine and will not dress inappropriately.

C4 is indeed the ‘middle’ C on a standard 88 key piano. That is where that convention comes from.
However, the pianoforte was invented in 1700 and by no means is it the first keyboard.... some two thousand years earlier in 300 BC, the first keyboard (the organ) was invented. It featured a 61 key keyboard, sometime several of them... in this oldest of key length conventions, the third C is actually the middle C (in addition to being the middle Key).

It is not a matter of right or wrong but simply knowing which convention is being used. To think one is correct and the other is not, shows a limited view of the world... it is simply a convention. Yamaha uses middle C = C3 (the first product the company made back in 1887 was an organ... it was not until just after 1900 that Mr. Yamaha started piano making).

49 Keys does not have a standard as far as I know (and is a convenient modern format for folks using the keys mainly for data entry purposes (I know of no musical repertoire for 49 note keyboards). But I would image all such keyboards made will come with Octave transpose buttons... which are fairly intuitive to use.

The mythological MIDI KEYBOARD has 128 Notes. You can map sound effects to the extra notes, or use them to control lighting or other tasks needed in the performance of music. This means that according to the convention to which Yamaha adheres (middle “C” = C3) the 128 note MIDI range goes from C-2 through G8...
88 key Acoustic Piano A-1 through C7
61 key standard Organ C1 through C6
76 key E0 through G6 (largest modern keyboard that can sit on the back seat of a standard sedan without sticking out of the window).

Thanks for your responses. In the end it is not super important where the middle C is located on MX49 as changing octaves is so fast. It is easy to set the octave shift so that is stays this way after restart. I am generally very pleased with my MX49. I use it as a desk-top-keyboard right in front of my computer (MacBook Pro with Logic, Synthesia as well as with iOS apps) and when I travel for its portability. To practice piano I have Casio Privia PX-870 that is currently residing in our living room. Considering my studio upgrade to "real keyboard" most likely with CP88. I live in Sweden in the forest with no access to shops therefore such discussion groups are very important to me when making buying decisions.

I know of no musical repertoire for 49 note keyboards

I don't know about classical repertoire, but sub-61s have been common for a long enough time, there are plenty of keyboard parts composed for 37-key mellotrons, 44-key minimoogs, etc. Lots of Hammond organs (M3 etc.) with 44-key manuals. Melodicas. 😉 So yeah, there are plenty of keyboard parts that play perfectly well from a 49-key board (or a 49-key top board in a stack). As well as, of course, playing string/brass/wind lines, since the ranges of those instruments' parts usually fall well within the 49-note range. MX49 can be a great upper tier gigging board if you're looking to assemble a super-light 2-board rig.

I just said that I don’t know of any... and although you say there are many, I see you don’t know the names of any either 😉
But not my point at all...
My point was there is no particular standard octave setting for the 49, 44, 37 or 25 note keyboards... can you write great music with less than 61 keys? Absolutely. Do they exist - like you say there are plenty... I just made a point about I don’t know any specifically written for that length. The Octave button is a must on all sub 61 note keyboards... so the user can concentrate on the range they need.

Humorously, only piano-centric keyboard players want or even demand to have such range (88-keys) at their command.
A 25-key is more than enough to do drums (I only knew of one drummer with a more than 25-piece Kit!)
When the Wind MIDI Controller (WX7) first hit the market back in the late ‘80s — the initial resistance to the product by Sax players was that they thought it was going to replace them. Once they realized that that was not the case (you actually needed to be able to play a wind instrument to play it)... but once you finally got them to try it, and once you finally got them over the saxophone sound-thing... the thing they enjoyed the most was the range... it had a ton of octave keys — and that was what captured their imagination...

I remember one demonstrator we had, when asked it it did a saxophone, would lie and say “No, it doesn’t” ...of course it did, but to prevent Sax players from completely dismissing it before giving it a chance (which is what they all wanted to do) the demonstrator would begin his demo with a drum solo.

Watching horn player’s initial reactions was priceless... Smiles a mile wide, laughter, joy, suddenly, it was no longer a thing that would replace them, it was now something they wanted to try. In fact, they’d line up to experience it. Then slowly but surely the demo would work it’s way around to lead sounds and woodwinds and synthy possibilities... and he would introduce playing appropriate phrases for flute, oboe, bassoon, synth leads, shredding guitars, funky phat synth basses, etc., then in a dramatic display he would play these sounds across 8 octaves... the fingering was standard - so the learning curve for most Sax players was literally 15 minutes... the hardest part (and watching and listening to hundreds of Sax player’s initial experience) was stopping them from playing those 8 and half or 9 octave runs up and down the instrument.

I tell that to point out — I was not trying to look down on the keyboards with less than 61... for doing most instrument emulations (other than pianos and organs) those ranges are enough, more than enough...) but the OCT Transpose button is a given on those because you want to be able to concentrate on the specific range needed... And because while most instruments cover 2 or 3 octaves in most musical compositions, you don’t have a standard location for middle C (that I know of...) If you are doing principally bass lines — how many octaves do you need?

There are plenty of use cases for keyboards with 49 or less keys, I’m well aware of that. (And who buys them).

I just said that I don’t know of any... and although you say there are many, I see you don’t know the names of any either 😉

Oh, alright, Strawberry Fields Forever, Watcher of the Skies, and Court of the Crimson King. 😉

I have an MX49. It's not one of my more frequently used boards, but it has come in handy. The funny thing is, I never noticed anything about the location of middle C. Maybe because I wouldn't have used it for piano anyway. But whatever the designers picked worked for me, the sounds come up in what I think are probably their most useful ranges.

the sounds come up in what I think are probably their most useful ranges.

I realized that some bass sound saved one octave higher like normaly in ROM presets on MX49. (This not a Performance setup, then it comes out when you change voice presets in bass category.)

After all, I hate it the most that the parts can't be shifted independently, only the "less fortunate" note shift function in edit mode and it jumps back suddenly when changing a part voice preset. )-:

76 key E0 through G6 (largest modern keyboard that can sit on the back seat of a standard sedan without sticking out of the window).

Dear Bad Minster, do you know anything about, why did it happen that way that octave keys range is based on E to G scheme on 76 note keyboards?
Some brand like Korg make more useful entire 6 octave keyboards C to C. It is often more necessary to use lower octaves than those above 5th octaves. This is consistent opinion of a lot of musicians interestingly.

the sounds come up in what I think are probably their most useful ranges.

I realized that some bass sound saved one octave higher like normaly in ROM presets on MX49.

I admit, I never used the MX49 for bass.

But your bringing up bass reminds me... Related to your point, I would say, though, that Yamaha does not necessarily optimize sound ranges for different size boards. The default bass split that happened when you hit the Split button on a MOXF6 made sense... but that button put the split and bass sound range in the same place on a MOXF8, which did not make sense for the default bass split, because you ended up with an extra octave of bass notes you'd never play on the far left, and then your right hand piano or whatever ended up with an octave fewer keys than it would have made sense to have. I suspect the 6 and the 8 simply had identical electronics/settings, as opposed to having some kind of alternate set of some of the basic parameters depending on whether those electronics were mated to the 61 or to the 88 where a lower split point and different bass octave range for the default split would probably have been more sensible for real world use.

Yamaha does not necessarily optimize sound ranges for different size boards

I completely agree with these.
Nay! Most voices are also programmed with completely different dynamic sensitivities and volume levels. Formerly, I have already noticed these on my MO8. But it’s not Yamaha only who makes such a mistake. Therefore, most people have more confidence in DAWs and plugins these days.
It is likely that a manufacturer hired one sound designer in the past. Today, due to thousands of voices and arpeggios, I suspect this is team work already.