IMO, selling out is the def of being real to yourself, if what you want is a good amount of money. I'm pretty sure that's what everyone wants... cash money. Keeping shit "real" just means you're limiting what's going to be in your pocket.
I mean, even DMX did Party Up.
Being "about the music" is just something a guy who isn't well known says to justify why he's still "underground". If you're "about the music" then you're in it for the art.
Art is free, mostly. Art is something you see or hear for free. When art has a price tag on it, and it's in "mass" production, it's a fucking product. Art does not equal product to me.
I've talked about this in depth with a few people and it's one of those things that never really have a definitive answer.