Yay, free stuff -- but that's beside the point. The point is that GameStop is taking pre-orders on downloadable content. Isn't the reason for pre-ordering to secure a copy in case the store runs out of stock? Not ... really a problem for DLC. It would seem that GameStop's strategy for dealing with a scarcity-free market is to hope nobody notices the lack of scarcity.
The best part: This offer is available in-store, but doesn't appear on GameStop's website. So you have to go to GameStop to pre-order the DLC, and then go to GameStop again so you can get the code to download your map pack from Xbox Live. Unless you're a Power-Up Rewards member, in which case you only have to visit a GameStop once, and then the code is available to you online. That's ... more convenient.