I actually don't quite agree with you. Nobody kept you from placing your pre-order early when it was still $10 credit, so you can't really say it's "unfair" when you didn't.
That aside, I think it was not intentional on Amazon's part to give $10+$15 credit for early pre-orders, my guess is it's...
Also only $15 for me -- which is ok, since what I originally expected. However, I can't help but think that we would have actually gotten the extra $10 if it hadn't been for all these folks here contacting Amazon... ;)
So apparently the Amazon price dropped to $59 for a few hours yesterday night? Shouldn't that fall under the preorder price guarantee? My invoice still says $59.99...
And yes, it's only 99 cents, but it's about the principle! :P