In-app option required, but not exclusive
Instead, as Paczkowski explained, "Apple wants its cut on sales enabled by its iOS devices, it has an established guideline that allows it to take it and thats what its doing.
"Developers are still free to send customers to their own Web stores, but they must also offer them the option of purchasing content within their apps themselves, and they must route those sales through Apple which will then take its percentage."
This harmonizes with Apple's previous policy, enabling users to buy through iTunes (and allowing Apple to earn a cut for facilitating the convenience) without forcing all content to be purchased within iTunes. For example, Amazon can sell Kindle-DRM ebooks directly from its website or through its own Kindle device, and iOS Kindle app users can sync those purchases to their iPhone, iPod touch, or iPad.
Apple has never supported in-app sales of content within apps that bypass its iTunes payment system however, an issue that has irritated the music labels, movie studios, newspaper and magazine publishers, and now, Sony's Reader business.