Well it does say the demo is coming to Steam too, so we'll see what "Windows XP is unsupported" really means. I'm really surprised they did this, considering in the most recent hardware survey that Steam took about 48% of people were still on Windows XP.
This might be enough for me to finally install the copy of Windows Vista that has been sitting next to me for years, but I really doubt it.
Sadly, I'm not surprised. They are probably receiving some sort money from Msoft to do it this way. With the first game the XBOX360 version was the real version of the game, with slightly better graphics and such. The PC version didn't even support widescreen (which is silly considering the XBOX360 version was obviously HD so obviously widescreen was in at least that version of the game).
So, I'm sure it is some sort of crap like that.
Though, I just recently upgraded to Win7 two weeks ago so it doesn't bother me any. Which, if you have the cash to upgrade, I would recommend it. I am loving it so far.