I can see Bad Company 2 crush MW2 on PC easily:
BC2 was #1 Top Seller on Steam last week (and still is), and there's still 5 weeks before it comes out. It is also in D2D's Top 10 and selling in other digital stores.
MW2, which had disappointing sales on PC, was only #3 in it's first pre-order week on Steam, and had only 2 or 3 weeks of pre-order. It also isn't being sold anywhere else other than Steam.