The explanation given when they put this policy in effect 2 years ago was that they hadn't decided on what they wanted to do in the mobile space yet and they just wanted to make sure nobody moved ahead without them.  It's been 2 years and this is still their policy, so they must really be struggling over whether they want people to be able to give them money from mobile devices.  Even something like this, with using Amazon data, fosters a much more active and healthy market that Amazon benefits from.  That kind of thing is intangible, though, and businesspeople can be stupendous boneheads when it comes to such things.  They assume the market is always open and active, with people integrating media products into their lives, regardless of what happens.  They're wrong, and Amazons business will hurt if they make it more difficult for people to read about products Amazon carries (even if Amazon is not mentioned at any point).  If some other source steps up, the market will still be helped, but Amazon will be left out in the cold as far as the information they currently gather from usage of their API, so it will end up hurting them one way or another.