Do I believe that Amazon is working hard to charge customers less for the good of the customer? Not for a moment. Amazon is a publicly traded stock. Like any for-profit company, their goal is to make a profit. And as this article says: “Analysts quickly observed that Amazon is likely selling its new tablet for significantly below manufacturing cost. Another commenter notes that the tablet's browser gives Amazon an unfiltered window into how users shop and transact.”
Plus, if you buy a Kindle, the only place you can buy ebooks for that Kindle is Amazon (although that might not be true for books out of copyright).
Amazon is not only selling you the contents of the books and the way that you read them, but more and more, it is also the publisher, as you can read here.