It's fine for App Store developers to complain about their costs of doing business like any other business. I'm not sure what the point of bringing up nonsensical hypotheticals like bank payments is.
Except this is a clear racket and not a regular cost of doing business. Imagine Microsoft tomorrow deciding to require 30% of even a fraction of things happing on windows. Imagine Apple trying to do this on the Mac. It's laughably anti-competitive and the only reason they're not doing it on the Mac is because it would expose the absurdity of the situation on iOS.
That, and Apple probably requires a shit load of third party utilities that do "naughty" things like read the file system or be "not sandboxed" in order to actually get any work done. They need the Mac to write APIs to charge people 30% on the App Store for the iPhone.
