So is MS just paying these four "teams" to do this as a marketing tool to proove how XNA can be used?
If so, it's a waste of money.
Sure it's cool to know you can make a game in 4 days with XNA if you really wanted to, but there should be more of a point to it. Like, how about all 4 of the games are released as a free download on XBLA for all us gamers to see? Not only would that be very do-able for MS, and cool, but it would inspire all of us sitting at home to get XNA ourselves and show we can make a better game. This would mean this "4 day challenge" would serve 2 more purposes: A useful challenge to all XBL subscribers since we'd be able to play them, and it'd be a great marketing tool for XNA as it would cause tons of us XBL people to sign up.
Simply creating this 4-day challenge for the sake of GDC is ridiculous. But hey, MS has money to waste so I guess that's fine.