the term is pretty stupid (IMHO) and has been thrown around for many years. On one hand, there are people that don't like a 'new' sound and they call the artist or band a bunch of sellouts
On the other hand, I've seen plenty of people say a band is a bunch of sellouts for allowing their music to be used commercially.
Yeah, that's pretty ****ing dumb if you ask me. A band gets their music played to a wider audience is good for everyone, unless you're some upity snobbish hipster-type. In which, case, I couldn't care less what you say at that point.
If I'm watching TV and I see a Cadillac commercial with a Beatles or Zeppelin track playing in the background, I think "cool". If I go to a sporting event and the beginning of Crazy Train is being played right before the start of a play, I'm happy with that. I sure as hell don't consider that "selling out" although some snobs seem to think so.