John Davidson was talking about this on the 1up podcast (which is kind of entertaining because it's just four guys getting wasted and talking/cursing/ranting about games for 45 minutes). He said it's in their contract that they're fully independent, and free to criticize as they wish.
But with MS looking to position windows as a gaming platform marketed like consoles are (unified packaging, in-store demo kisks, etc.) they said it was a good way to get in with that.
And/or get paid. Whichever.
