I can testify to the fact that they won't. They had a low-ball price for Defenders of the Faith, and when the correct price came along, they simply sent an e-mail out that said it had changed, and gave the option of cancelling the order. I cancelled the order. I think a few folk here had the same experience, and only a couple of them got Amazon to honor the original price. Others were just told, effectively, "too bad."
Wow, that's KRAZY cheap. I'd order it, except that I'm fanatically loyal to my local game shop and (more importantly) I want it on the first day and refuse to wait for shipping.
According to Amazon.com the Epic book is only 128 pages. So that explains why it is so cheap. However, WotC has updated their info telling us that the book will be over 300 pages. Amazon.com just hasn't updated their info. I'm sure the price will change once the page count does.