I just finished watching an Eric Clapton concert of a few years ago...both keyboard players, Billy Preston and David Sancious were using 88 note keyboards(Billy also had a B-3)...Sancious even did a "Sax" solo (using a breath controller) on his 88 note weighted hammer instrument, so I guess that some are capable of using other sounds with weighted keys.

The sound I find hardest to use on an 88 note weighted action controller/keyboard is organ (slides and smears are difficult)...61 unweighted are perfect for
that technique.

Sure, if you have to use one keyboard for it all, I imagine a 76 note semi-weighted instrument would do...but, it would most definitely be a compromise if your main axe was piano.

I still see far more 88's than 76 note instruments.

Ian