This is only the beginning, and was all telegraphed a week or two ago. Sony dropped support for their ebook store on iOS devices because of this exact rumor, that Apple was going to start insisting that Sony had to sell their books in the app and give Apple a 30% cut, and also couldn't charge more (you know, 30% more) in their app than they did elsewhere.

At the time, people were wondering what this meant for the Kindle app. There's rumblings that Apple would place the same restrictions on Amazon, saying that they had to sell their books through the app only (currently the app opens to the Amazon's site, I believe), they would give Apple a 30% cut, and Amazon wouldn't be allowed to sell their books in their iOS app for more than they did elsewhere.

So, continuing these possibilities, what if Amazon pulled their Kindle app from iOS? That would be an enormous hit to iPad sales, as good as they are, and be a big boon to Android tablets.