There are lots of ways to look at it - in another thread someone said it should be treated like macOS or Windows and I replied:
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I understand the macOS comparison. However, we have two precedents here.
The PC open market was long established in the 80s.
Then games consoles came along, and you had to buy the specific cartridge that fit that hardware to release your software. You couldn't make your own cartridges; you had to license them through the console maker. You could make the same argument that they made their money selling the machine in the first place here too. The split in their setup was largely considered to be 70/30. This then applied to disc based systems later with Playstation, Xbox and Nintendo - the same 70/30 split.
This progressed into online consoles and online web stores. So now we have PlayStation’s online store, the Microsoft store for Xbox, Nintendo has a store. Before that, we had Steam, who set up arguably the first online digital store with a 30% digital split. Everyone else followed.
After Apple did it in 2008, Google did it a bit later also with a 30% split. Then followed Amazon's app store, Microsoft store, all the games stores mentioned, Meta Quest's store - all at a 30% split.
It's largely built around the bricks-and-mortar shop idea where they'd hope to make 30% (though it'll be a lot less these days) - so that's why EVERYONE does it, not just Apple.
Of course, the Epic store is the standout difference, and that's why Tim Sweeney pushes everyone as wrong because he's realised they can make a fortune at 12% and try to get everyone to side with the man who makes billions selling children pixels in a computer game every year as "skins" as if he's the arbiter of morality.
So the argument falls on: is the iPhone more of a Mac or PC, or is it more like all the other devices mentioned above? Apple have a very good argument for the latter as every other mobile device, phone, gadget, games console, consumer electronic falls under the latter.