It seems to me that musicians play more complicated things the easier the instrument is, so it does even out at the end. Drummers do some insane things, even though they only have five drums to hit (whereas a piano has 60ish keys).
I agree with your general point. So maybe the following is the exception that proves the rule, but:
An acoustic piano has 88 keys, and classical or jazz piano music tends use many of them. Whereas a 60 key electronic keyboard is often subject to the Flock of Seagulls treatment, wherein one key at a time is held down. :) It's roughly like touch typing vs. hunt and peck.
But aside from that example, yes, I think you're onto something.
