Because this press release also updates and clarifies enforcement of in-app purchases as well. The current approach taken by the Kindle app, that is, linking to

Because this press release also updates and clarifies enforcement of in-app purchases as well. The current approach taken by the Kindle app, that is, linking to the Amazon web Kindle store for purchases, will no longer be allowed by Apple. Apple will force Amazon to allow users to purchase ebooks in the app, taking a 30% cut.