All of those devices are likely sold at a loss or a very small profit margin though (at least when they are brand new), and they aren't any more powerful than current phones (and don't have cellular radios, front and read cameras, CDMA licensing fees, etc). Amazon uses their own app store exclusively, and so does Barnes and Noble. Each developer has to pay them $25 a year to be listed, and they also get a cut of the app (and obviously book) sales.