I've got to admit; I'm not a fan of U2 at all. A lot of their songs I find to be unbearable to listen to. Because of this, I can't say that I clearly understand the topic at hand.
Simply put, how has U2 helped to 'redefine' rock, and 'change' the face or R&R. I just don't see it, at all!
On another note, Somedude, I don't agree with your very last statement. I dont think that U2 has the second 'biggest fanbase' in rock and roll history. I feel that there are many other bands, current or not, that have/had bigger fanbases. To say that U2 is basically the second biggest band in the world is, in my opinion, foolish. There have got to be many more bands in the world, that are more popular than U2.