No one is saying the App Store isn’t very profitable for Apple. Just countering the misinformation from n the original post and the blatantly wrong assumption that the App Stores only costs are payment processing.
Disclosure: I’m a long tine App Store developer.
Also, you are talking about the margins on all Apple's services, some of which are much more expensive than others. The margins that other digital software stores can charge suggest to me that they can be very profitable without the 30% cut.
Full disclosure: I am a longtime Apple shareholder.