First, don't trust AMAZON for publishing information... ever! They have screwed up so many times it makes me physically ill that a business can be that wrong and still be running. Trust the official SRD site that is coming soon. THAT source will be official.
Second, the book won't be 896 pages. It will be several hundred less than that, I guarantee it. Why do I know this? A few reasons, but the most important is: DO NOT TRUST AMAZON FOR INFORMATION! Don't get riled up over this. Get riled up after Steve has edited the manuscript and knows finally how many pages it will be in manuscript form, then how many pages it will be in publisher book layout form.
Finally... relax! There are plenty of great books out there to read. This one is one of them, trust me. Just realize that we have an entire 10 months to go at the minimum, and A LOT is going to happen in those 10 months to make the fans happy.

Ard Rhys