I'm agnostic. I'd like to believe there is a God, and I think I could have faith in God. But I could never subscribe to religion. Much like Bono says that people die by accident of birth, I refuse to believe that certain people wouldn't get into heaven (if it exists) by accident of birth (i.e, born in another country, so they're not christian. Or born in America, so they're not Muslim for example).
So, I love U2 music, and I can understand their spirituality by the fact that they come from a different upbringing. I can accept them, because they accept everyone (ex. COEXIST). Even if Bono is singing "jesus 'round my neck." or singing about "the magnificent." Both songs which I love.
For disclosure's sake... I was brought up in a catholic household so that also might make their music more palatable to me. I will say though, that if and when their music does become overtly christian, I have to think about the song a little bit to see if I accept it not. So far, I've accepted everything I've heard.
But, I don't think I'd ever choose to listen to a Christian Rock band otherwise. Because to me, those bands are making music for the glory of Jesus Christ, and I'm just not interested.
U2 seems to have a wider variety of topics to create music about, though God is a part of it, and I don't think they're a "Christian Rock" band in the sense that I'm talking about it.