I don't understand, what does screenshots of Halo 2 (old by now) have to do with Vista or DX10?
The sad thing is, this has everything to do with Vista and DX 10.In fact, it's what Microsoft has been toting so far as one of their few "exciting" Microsoft-published answers for "Why to buy Vista for the new wave of games"... except for Flight Simulator 10, which - though very nice looking in DX 10 - is a bit of a niche thing.
The game requires Windows Vista, because it's so incredibly advanced and all. ("Hmm," says the dumb user who they are trying to fool, "it looks like Windows XP has better graphics and newer games than Windows Vista. Why do I want that thing?")
Nothing against Vista, just their strategy: "I know, let's re-release console games that should have been on this platform 3 years ago, charge for them as though they're new and use them so people buy our operating system!"