I can't help but feel that some of these choices were influenced by the popularity of the track and the game itself rather than how good the music is.
I mean, really, the Super Mario Bros. theme? Sure, it's pretty catchy and more or less everyone who plays video games knows it, but is it actually that great a piece of music in and of itself? I certainly don't find it as impressive as Wily 2, for instance.
Maybe I'm just bitter that Calling from Heaven isn't on there anywhere, though. Why has nobody remixed that yet?