Interesting point - you hear the same thing from photographers. Its one thing taking photos in your spare time and trying to be creative or take "good" pictures (as I do) but if I was taking them all day everyday - wedding pictures, baby snaps etc... I think I'd be so sick of the camera at the end of the day that I'd never do anything for myself. Likewise with music - being under pressure to produce "output" would be a total turn off.
Ooh look, I'm rambling too...!