I have read rumors the Diablo III: Book of Cain was delayed, and comments in reaction to those rumors. Today, Sunday Dec 11th, I reached out to Insight Editions publicity manager, and she replied in half an hour.
The rumors are just that. Diablo III Book of Cain will be released on track on December 13th. Amazon is currently in the process to fix this in their system. Please, let your communities know the accurate info.
Those who haven't yet heard of Diablo III: Book of Cain, check out our info sources: