Most POD (Print On Demand) publishers do not own printing equipment. Instead, they pay a printer to print a certain number of copies. Amazon, happens to own one such printer. It's called BookSurge.
Amazon has recently told a number of POD publishers that if their books aren't printed by BooKSurge, Amazon.com won't carry the books*. Amazon has already followed through on this threat with a publisher called PublishAmerica. Here
is a list of books that publisher has on Amazon. Check it. See how many are being sold by Amazon.
I don't know about you, but I'm pissed.