Actually, I believe that Roland and Korg are more mucially correct than Yamaha and Technics. For example:
In simple, one finger mode (Roland) a single note gives you a major chord of the same name.
eg: "G" = G maj chord
Apply your musical theory and know that to make a minor chord you need to flatten the third degree of the chord ("B" in this case)
so play:
"G" and "Bb" and get the G min chord.

Who ever decided that playing ANY black note to the left of a tonic, makes musical sense was drinking on the job, I think!
It is much more logical to use correct musical theory when forming chords ... even in the simple fashion.

C + Eb = C Min(Roland/Korg)
C + Eb = Eb7 (Technics/Yamaha)
Sorry, but that's just goofy.

All major makers seem to act the same if 3 notes are used at a time, but it's this one and two finger approach that differs from brand to brand. Just like the "interpretation" of what FULL size piano keys are. Roland , Technics & Korg have it right .... Yamaha is making a fashion statement like the Cooper Mini car. Smaller is better, they think.

I disagree.