it's all marketing. bands are labeled as "Christian" so they can be sold in Christian bookstores and uninformed parents will let their kids buy anyting from a "sanctioned' bookstore. sadly, the majority of evangelicals find art that explicity references their paradigm of Chrisitianity as the only worthwhile art. u2 has been smart enough to stay away from being labeled as such. the sad part is bands like the 77s, Adam Again, the Choir and Daniel Amos were bands that came out during the 80s that were incredible bands that were never noticed in the mainstream because they had the "Christian" label, but were not "Christian" enough in their lyricas, actions, look, etc. to be fully embraced by the narrow-minded CCM market. today it's quite a bit different. there are more opportunities in the CCM world, but it has now become a place to market an act that's already been proven in the mass market. nothing too original in the CCM world. i'm so glad U2 did all it could to stay away fron the "Christian Band" label.
I attend one of those evangelical mega-churches and i'm in the middle of this subculture that is fascinated by explicit art and "signs" of Christianity. I think it's a reflex reaction to the American culture becoming more secular. They feel comfortable in their bubble, but have trouble being "in the world, but not of the world". it's easier to remain in the bubble. and thank goodness U2 is not part of the bubble or they could have been dealt the same fate as the 77s.