"In the short run, I can't imagine users would care very much if they could only get their books from apple and not amazon, and it would probably help Apple lock in users."

Have you had any actual users actually tell you this?

Everyone has heard of Amazon, everyone knows Amazon has lots of books, everyone knows Amazon has pretty competitive pricing, and most people who would consider buying an iPhone or iPad have probably also heard of Kindle. Having one device that can read Kindle books and also do a lot of other stuff is part of the current value proposition of iOS devices. If that goes away, it will inform the buying decisions of people in Apple's target markets very quickly.

Just imagine the next Walt Mossberg reviews, comparing Android and iOS devices, pointing out that you can read all your Kindle books on Android, but no longer on iOS. That's not going to immediately affect sales?

Heck, much of Apple's target market may already be hearing this news and taking it into consideration before deciding to buy an iOS device, because they are consulting their geek friends about the decision.

I know you said you think this will happen "in the long run", but I think it could affect Apple's sales much more quickly than you expect.