I have some questions, and I don't have the answers:
Why is West Side Story a piece of musical theatre, but Symphonic Dances from "West Side Story" a piece of classical music? Why is Radiohead rock, but Christopher O'Riley's albums of Radiohead music classical? Just what exactly is John Adams' I Was Looking at the Ceiling and Then I Saw the Sky?
Should we eliminate musical genre terms, as David Lang wrote, partly because they're dictated to us from others? Do they help us fulfill a human desire to categorize? Would it be easier to shop (virtually or in a brick and mortar store) if CDs were organized by artist, regardless of genre (as Christian McBride, I believe, described in a record store in Philadelphia)?