it depends. seemingly apple offers a bit more than a payment service, that's why is used the word "payment experience". and not just that:
- unified currency handling
- taxation handling
- 1 click secure payment with biometric authorisation, that can be backed with multiple payment frontends (like carrier subscription, e.g. not a debit/credit card)
- solid and well maintained codebase for the payment service with no external dependency.
- simplified user login
- discoverability
and that's for 15%, not 30%
everyone has the right to create a web/db/google campaign to promote their dating service, offering registration and subscription service on that website, even a link to the app store where one can download the free app from apple, that will ask the user for login to access the 'premium' section. and it will pass app store review, etc. and it can be operated w/o giving apple a cut from the subscription fee that has been collected *independently* from the apple app ecosystem.
yet developers choose to use the IAP solution from apple and cough up the 15%. there must be a reason for it, right?