I'm not really sure who this is aimed at, since the majority of games are crossplatform now, anyway. If it's for a game that is, why would I spend $59 for the Xbox version when I could get it for $49 or less, as generally most PC games are cheaper initially, and get rapidly cheaper still. If I already own both an Xbox and a PC, I guess the one upside is not having to buy it twice if you wanted to play it on both platforms, but I wonder how often that happens?
This may indicate Microsoft trying to get more exclusives, so that if you buy the new Xbox game you'll also have it to play on your PC, effectively having a two platform exclusive, both of which they control. Otherwise, it seems like a strange feature to try and shoehorn in, doubly so if you've got to pay extra for it, and stranger still if I'd have to pay for both GFWL and XBL Gold.
That still doesn't explain why I'd want to be able to play MW or Arkham Asylum on my PC, when those are games I specifically bought to play on my 360. The really annoying prospect is that they could just stop releasing Xbox games for the PC independently at all, and leave us having to pay inflated prices for a dubious benefit.