It would violate the store’s agreement with the distributor, and stores work very hard to avoid this kind of thing. It is remotely possible that an unethical store employee might slip one out to his or her friends or someone who bribed him or her, but a store is not going to make anything available before its release date.

There was a local video game store in my city (he just closed his doors in the last month) that would sell games long before they were to be released. He sold Halo 3 about a week early, more for GTA IV, and Call of Duty: Modern Warfare 2 was available a few weeks before it was released.

So yes, the items are in the store, but they shouldn’t be on the shelves before the formal release date.