Stores give things to people who reserve as incentives, probably because by selling all copies on the first date they can demand more shipments sooner and sell more games more quickly.
With games like this one, there's no incentive needed...several people have reserved it since last year, and several more have done so in the recent months. Nonetheless, some stores give little bonuses, such as that hat. The Gamestops in my area offer a cheaper strategy guide. Depends on the store.