Its' kinda funny, because Amazon's price comparison stuff is patented six ways from sunday. They make a ton of money via arbitage and finding the lowest price that you (yes, you, person reading this) would be willing to pay. Depending on who you are, where you live, and what you've bought.. your price for books and other things are different than mine. It's all a very, very intricate system that is built to squeeze the last dime from everyone.
Ever wonder why , when you're looking at a book recommended in a forum or blog that it seems like the cost isn't too bad (especially in pbooks or ebooks where the publisher hasn't demand set a price?) and you almost click that button? It's because Amazon knows you.