It is much harder for me to trust Gamestop when it comes to this sort of pre-order. They give you no confirmation that you will recieve the item on your invoice. And they make it quite clear that the bonus will be in limited supply.
The fact that Amazon actually switches off the limited-edition version of the item when they have hit the limits of the units they have been promised is more encouraging. It makes it seem that they are taking the limited nature of the item more seriously.
I've never actually had a problem with not getting a pre-order bonus with GS, even when they don't list it. But I definitely get where you're coming from, in case you don't get it it'd be hard to argue.