nothing to do with proprietary anythng...its simply how synthesis works, as i said in the old days the oscillator produced a tone (saw, square, triangle) ad then through subtractive synthesis you created your sound...one oscillator created one sound, or a monophonic keyboard, then they started installing more oscillators as technology increased...these days ONE sample (the equivalentof ONE oscillator) is assigned to ONE sound ( the stereo doe not come into it) stereo simply means they have allocated 2 sounds split over the left/ right fields,it still uses 2 voices to produce the sound...you don't have to believe me just look at your yamaha manuals, although perhaps the home arranger keyboard manuals dont go into the detail on how the sounds are allocated, as do the synth (Motif etc) ones...just ask your yamaha techie, they'll tell you the same thing...its no big proprietary secret...the voice allocation algorithms for each manufacturer ARE though..
and yes, i can count to 32 as well