1armedband - I see where you're coming from and to a large extent, I'd agree with you. But just occasionally someone does a cover version that knocks spots off the original, or at least matches it. Jeff Buckley's rendition of Hallelujah, for instance.
And also, if bands didn't do cover versions, we wouldn't be able to go to pubs and clubs and listen to our favourite songs for a fraction of the price (or even free) - and as I've said, they're not all bad.
And we wouldn't have karaoke either ... although that's maybe not such a bad thing. ;-)