Amazon gives you a fair deal and lets you know they can terminate their promotion at any time. I just thought it would be helpful to most people to know that your $20 credit is more like a coupon than a video games gift card. It has a short expiration time.
After you purchase a pre-order with this promotion, you'll get an email letting you know that you have a $20 credit that will expire two months from your original purchase. For those that buy video games frequently this isn't a problem. For others I recommend Walmart's pre-order for Metroid, that offers the same $20 web credit, but without an expiration date. Even with a little tax, it's better than having your credit expire on you