A lot of people use the Kindle iOS app. Imagine if Apple pulls it from the App Store, and Amazon inconveniently launches a $199 iPad alternative that includes it and more.

In the long run, it would probably be great for Apple: iBooks would become the only widely used commercial-ebook reader on the platform, and iOS devices have such a massive installed base that being the exclusive vendor would give Apple a huge advantage when negotiating with publishers to be in the iBookstore. Amazon knows this.

But it would cause a pretty big short-term headache for Apple that, if there’s a new and very inexpensive tablet alternative from Amazon, could pose a credible (although almost certainly not fatal) threat to the iPad’s marketshare. And Apple knows this.

I suspect the Kindle app will continue being mysteriously and indefinitely exempted from the in-app-purchase rules.

• Not being locked into a single hardware platform is a big selling point for Kindle content. If it wasn’t available on iOS, it would decrease its appeal.
• On the other hand, as soon as you own Kindle content, you depend on your device supporting it. And iOS would be less attractive to you without the Kindle app.