Far be it from me to try to define art, but at some point I imagine an artist must stop and ask him/herself "Is my work an original thought? Am I telling a story here, sending a message, engaging with an idea, being provocative, being honest, making my audience feel something, or is my work... mass-produced background mall muzak? A soulless sculpture for some corporate headquarters?" Pop music has always been right in the middle, toeing close to that line between "mostly art" and "mostly commercial product". Where the difference between what the artist wants to say and what the audience wants to see/hear is blurry. I'm sure when you enter that world, surrounded by producers, business people, investors, execs, marketing, focus groups, event organizers, you feel the pressure to go along with the flow and just build a formulaic consumer product.

I don't think art that doesn't sell is lesser than art that does sell. I know, tell that to an artist who wants to make a living... but I really think you have to measure a work along more than one axis. How good something sells is a different dimension than how good something is. If that wasn't true, Thriller would be the best music ever and the Toyota Corolla would be the best car in the world.