This is the same strategy that Apple pursued for dating apps in the Netherlands, after a court there forced them to allow third-party payments a year or two ago. Their argument is that the 15/30% is a general fee for use of their infrastructure (App Store, etc), and so they'll subtract the approximate cost of payment processing if you're handling it yourself but you'll still have to pay the rest of the fee to them. A…
What’s the egregious bit? Because Apple were so successful with their product they should have a cap on how much they capitalise? Do you get upset at business class in airlines? Or cinema food being so expensive? Isn’t this the point of capitalism?
I'd tend to think of the Mac as the most-direct comparison point, where there's the App Store but also where a developer who wants to handle everything themselves can.