Valve games on PC and steam. Better optimized and cheaper.
Bought on steam L4F for $25 2 months after launch. While 360 owner bought by 50-60.
360 have to pay $50 a years to play online on L4D.
360 owners have to pay $7 for add-on.
PC is add-on is free, online is free
Free dedicated servers, mods, community servers.
And didn't even touched on Orange box.
Buying Valve games without steam is newbish.