Preorders don't have the $10 deal link attached to them, unlike released games $39.99 and up.
Since Modern Warfare 2 is a game I planned on getting (basically) Day One, this was a good deal for me. Got Street Fighter IV in-store for $30 (plus tax). I hear it's a halfway decent game.
P.S. While they might be able to look up your preorder with your Reward Zone purchase, if you take advantage of this in-store, my advice is to take the receipt, put it in the preorder empty snapcase, and throw that sucker in your sock drawer for the next six months. Sure, it's only five bucks and you'll certainly be able to get the game Day One even without it, but losing it kind of defeats the purpose of the deal, no?
P.P.S. I have to say, unless one plans on taking advantage of this for a critically-acclaimed game like Street Fighter IV that's already on sale, I can't really recommend the deal. Best Buy is pretty much significantly overpriced for most games that have been out for more than a couple months. Gotta be a "devil customer", you know.