George, perhaps we are confusing length with width, or perhaps I do not succeed to explain myself, because english is not my language.

I measured both keyboards and I can assure that the total distance since the first key to the last key is one inch less in PA50 than PA80, because PA50 keys are narrower. An octave in PA50 is 1/5 inch less, and so the five octaves measure one inch less in PA50.

Another different thing is if the keys are longer or shorter, as you say. But I did not speak of that. I speak of keys width, the distance of each key to the following one. And I say that PA50 keys are narrower, they are of same size (that is, narrower) that those typical "smaller" PSR keys. And PA80 keys are wider, they have same size that all Rolands or acoustic pianos.

PA50,60,80 have similar sounds, styles. But while PA60 is exactly the same built PA80 (but black) without some internal things, PA50 isn't; it may seem a PA60 because their functions are similar, but it isn't a PA60 at all. Both have different keys and weight: PA50 weighs a 20% less!! Why?.

Dimensions:
PA80 & PA60: 43,7"(W) - 15,3"(D) - 6,45"(H)
PA50: 41,5"(W) - 15,47"(D) - 5,91"(H)
Weight:
PA80 (30,6 lbs) and PA60 (29,76) are very similar, but not PA50 (24,8 lbs)