> This ad changed their view and now though that the Kindle app on iOS was a promotion of how easy it was to move to Android.

I don't read it that way (most of your post I agree with though). I think the point was that before this email, Kindle devices had their own customers, and Apple wanted Kindle as a feature on their products to increase the appeal of iphone/ipad. But eventually those customers started doing all their "kindling" on their apple devices, so now from apple's perspective they think "we are providing you customers/making you a market, pay us". This is what the whole second paragraph is about.