Well, I didn't mean literally every band. I meant every band looking for commercial success--I realize there is a large difference. I don't know if a band can succeed by continuously changing their sound too much, or they risk losing members of their audience. We saw this with U2, who seemed to alienate many of their fans with Zooropa and Pop. Most bands just aren't willing to take that kind of risk. And really, they should be allowed to make whatever music they want to.
I admit I don't know much about Wilco, but they certainly don't sound like the type of band looking for huge commercial success. I applaud them for doing what they want to, but realize that in order to be a pop band, you usually have to write pop songs. Oasis have never been the type of band to make incredibly groundbreaking music, but rather straight ahead rock music that gets on the radio and that people can sing along to. Nothing wrong with that.
As for shamelessly borrowing, well Noel put it best saying "Why write your own tunes when you can nick someone else's?" They're not trying to hide it, so I figure just let them do what they need to. If the music's good, that's really all I care about.
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Change is the only constant