That is all incredibly irrelevant as Kindle, Nook, etc. are NOT paid apps! They are free Apps!
That they are and Apple allow those those app's to use content from places other than their store. I'll just remind you that this entire is entirely based on speculation. Apple haven't changed anything. Until they do it's all guess work.
Your mistake is that you seem to think paid & free apps are inherently different in the case of the above. They're not. The likes of Amazon still make money from that application from Apple's ecosystem. They're trying to piggy back on a product that isn't open so if Apple make the change they'll have to pay for it.
If they do make the change then the debate falls into what the rest of the app store has functioned like and my guess would be that some sort of a deal would be worked out with the likes of Amazon, like it appears to have been with Netflix.
1) This isn't how Apple's system works - that's obvious! Look at the current swathe of Apps that offer content like this - e.g. Kindle and Nook!
No they allow amazon to let their app to access the users content within their kindle account. They Don't allow Amazon to have in app purchases or anyone else without receiving a cut. All in app purchases go through Apple.
2) Android has the EXACT same business model as iOS - 30/70.
Yes. The entirety of Apple's iOS/App store business model is encapsulated in the 30/70 developer split isn't it.
It's the EXACT same thing.
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Apple don't have to allow content providers, many of them direct competitors to use an ecosystem they've invested the last 10 years into creating for free. They don't just create hardware, they don't just create the software, they don't just create the infrastructure that holds it together.... they create it all.
It's all controlled & fenced off but it's what gives the app store the value it currently has. Not just to Apple but to the entire developer community within the app store. It's why it's been the success it has.