Yesterday, Gizmodo reported on Sony's attempts to get a Sony Reader app approved by Apple:

Sony has told the New York Times that Apple blocked their Reader app, which would let users read their Sony books on iOS devices. Not for a weird reason like private API use, but according to Sony's digital reading president Steve Haber, Apple is mandating that "all in-app purchases" go through Apple.

This has been Apple's policy all along, and the Kindle and Nook apps get around this by going outside the app and linking directly to the web stores. And Apple has released a statement suggesting that this could be the start of an e-book war on the iPad:

Apple has responded to the furor over its supposed App Store policy changes that many believe could affect the popular Kindle, Nook, and Sony Reader apps. The company claims it has not changed any of its guidelines given to developers, but it indirectly confirms that accessing content purchased elsewhere could be a no-no if that content isn't also available to be purchased through Apple's own system.

"We have not changed our developer terms or guidelines," Apple spokesperson Trudy Muller told Ars. "We are now requiring that if an app offers customers the ability to purchase books outside of the app, that the same option is also available to customers from within the app with in-app purchase."

This is basically Apple demanding their cut of everything sold through apps on the iPad and iPhones, whether it's sold directly or not. There's no way in hell that Amazon is going to let Apple take 30% of every Kindle book sold on the iPad, so does that mean that Apple will reject the Kindle app? Is this an attempt to promote Apple's iBookstore at the expense of all the other readers on the iPad? This could get real messy, real quick.