It gets even more ridiculous if you consider that there are cases with price bindings (e.g. books) or small not very flexible margins (per song buying of music) and apple is them self competing in this area without this cuts.

Similar ridiculous is that they effective prevent apps which just provide the service for existing member without any payment/sign-up services in the apple app.

This is a active intrusion on the free marked undermining the fundamental concepts of it (choice and transparency). At least in my opinion.