But I think a fair question is: why are these performers even using sheet music? Imagine going to a pop concert and [insert favorite artist] was reading sheet music while dancing on stage. Shouldn't the music be in "muscle memory", even for classical performers? Wouldn't that open up more opportunities for contact between the performer and audience?
One difference is that Pink Floyd made their entire careers on about thirty-five songs, iirc. That's about one season's worth of one symphony orchestra's repertoire, and most performers perform with multiple ensembles to make a living. Does the wedding gig string quartet have their regular repertoire memorized? Probably. Does the orchestra have the premiere by a minor Midwestern composer memorized? No, and they never will.
Organ rather than piano, but the repertoire for a month of cathedral services (assuming daily Evensong plus Sunday morning Eucharist) is vast, especially considering all the registrations (stop selections). Playing all that from memory is unrealistic.
Here’s a typical month at Worcester, and bear in mind it doesn’t include the voluntaries at the start and end of each service (though the start will sometimes be improvised, at least in part): http://www.worcestercathedral.co.uk/media/October_Scheme_201...
That's an entirely fair question, and in a lot of piano auditions at least in my experience memorization is required. Most of the time, sheet music isn't helpful because it answers "what chord am I supposed to play next?" but more so as a roadmap for the structure of the piece. Take a look at the sheet music for the Stockhausen Klavierstucke mentioned in the article and you can see why this would be helpful.
