I'm not sure why it's not the same. Apple could just sell the hardware. Here Apple is selling the hardware and providing a marketplace for apps. There is virtually no difference between the App Store and using the browser to buy things from Amazon. The argument is that Apple should provide the ability to sell things on the App Store with out a cut. Amazon by the same argument should be forced to do the same.
You can argue that Amazons web Shopping market share is larger than Apple's cellphone market share and should be subject to the same monopoly regulation.
Apple distributes the app. They should be able to take a 30% cut for that if they wish.
However, my app has an unlimited subscription. Accepting payment for this is handled by Stripe. Once the app is on the users device, if a user subscribes to the unlimited plan, why should I have to pay 30% to Apple? They are not delivering that service in any way, shape, or form.
A better analogy would be that I buy a Nespresso machine on Amazon. Some of that goes to Amazon for facilitating the transaction and delivering it to me, some goes to Nespresso for actually making the device. Then I get a pod subscription from Nespresso. Amazon then says that because the machine was originally bought on Amazon, they are entitled to a 30% cut of that ongoing subscription price, even though the subscription is neither facilitated nor fulfilled by Amazon.
I think we can all agree that would be ridiculous. That is what Apple is doing.
You can argue that Amazons web Shopping market share is larger than Apple's cellphone market share and should be subject to the same monopoly regulation.