That's what Jay Yarow wrote in a Business Insider article today. And it's certainly plausible, given Apple past monopolistic behavior.From the article:
People who use the Kindle app on their iPhones today will know that this isn't a new thing: Since the Kindle iPhone app launched last March, users have had to leave the app to buy e-books.
Amazon didn't built the app this way from the beginning. We have learned that when Amazon first submitted its Kindle application for the iPhone to Apple, Amazon included its own payment system within the app, so customers could just pay for e-books and download them right in the app.
When Apple spotted the payment system, it told Amazon to get rid of it, according to a source familiar with Amazon's operations.
Why? It's a rule Apple smartly instituted at the App Store's beginning, forbidding third-party e-commerce of digital goods within apps.