Edit: clarification of Apple’s monopolising
No one can create a new App Store on iOS devices.
If you are referring to the App Store itself well no hardware device I can even think of, apart from a computer, allows competing stores.
Benefit of the doubt: Apple provides a great deal of value for app creators in the form of documentation, development software, a distribution network, payment provider, etc... all of which costs money.
their documentation is some of the worst out there. android on the other hand has some of the better documentation. that said i prefer apple products but as a dev their docs are woefully bad. basically just a dump of the class header comments and not enough conceptual documents coupled with some information is mentioned in the wwdc videos and basically nowhere else. The richest company on the planet could use to hire some technical writers.
I still consider it quite extortionate however considering app devs are adding to the ecosystem and potentially driving sales.
which merchant accounts are charging that? last i saw it was typically a transaction fee of ~35¢ and around a 2-3% fee on the rest.
For games (as it is a domain I know): Steam, Playstation Network, XBox all charge 30%.