Haven't bothered reading everything, but here's my own spin to it:
In a way I fully understand TJ's point. I have a bias against covering songs in one way. I feel like you're not contributing to the music world with your own material and just using other people's work. That said, when I perform it's never my own tunes - which makes me a complete hypocrite. However, the problem, with TJ's argument, is the fact that music=art and art is subjective meaning that there can be no "objective" better version of a certain song. (probably been brought up tons of times in the thread, but repetition can't hurt)
I just have to semi-rant a little though. I have a love-hate relationship for artists using other people's work. One fine example is an excellent saxophonist like Cannonball Adderley. He played with Miles Davis and then became a leader and one of the finest alto saxophonists ever. Yet almost none of his albums contain original material. He's taken a standard and played it his way, like his version of Autumn Leaves which I consider to be the greatest recording of that tune ever. For some reason, even though I enjoy the music a lot, the fact that few of his recordings contain his original songs, it's a little bit harder to enjoy. It's like, the tune has so many versions that you don't know how the composer actually "intended" for it to sound like.
Also, that "pure" is always best is complete BS. Symphony X - Masquerade. The original album version sucks bollocks, but the remake bonustrack included on The Odyssey is nothing short of a 5-minute eargasm.