its not really a new idea, Panasonic did the game for the gamecube called the Q (DVD player) and sega licensed out dreamcast technology out to other companies, (pace they guys that make the sky decoders bought a licence with the idea of downloading dreamcast games, but it never got past prototyping.
I don’t think your going to get differently powers Xboxs like you do with pcs, its would be more like the DVD player or VCR play. Yes they are all different, with extra features etc but fundamentally they all have to play all dvds or video tapes.
also it would not make sense to make games for only a more powerful xbox 360 version as the install base for the "normal" is nearly 20 million. I would think MS would have rules on how well it would have to run as well.
also MS have been making a profit on xbox hardware for a while now
that was back in Nov 2006, and since there has been further reduction is manufacturing costs and a price cut.