We've seen this many times, it's not exclusive to the case against Epic.
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Please note that I have not weighed in on whether I think Apple or Epic is in the right (legally or otherwise). I'm just informing you of their justification, and why they claim this isn't a danger for other developers who may accidentally (or, perhaps, much more minorly) break the terms of service.
I have no understanding for anyone that buys Apple and then complains.
One could, you know, make a case that it should be illegal, go to court to get that official, and then the way to implement your own payment processing is open.
But beginning at the last step, is totally the wrong order to do these kind of things.
Besides that, Epic and Apple had an agreement the moment Epic published fortnite in the app store. If they dont like the contract, they can leave. Again, if they think the terms are illegal, go fight that out BEFORE you implement something that breaks the contract.
Or what goes into each game console, my cable provider installs on their set top box, and so on.
I for one am happy to see Apple fire back with both barrels. Epic deserves it. A message has to be sent.