30% probably originated from brick n' mortar days where publishers were used to losing 30%+ and lobbyists probably ensured parity with digital stores to prevent publishers from withdrawing from physical sales. Everyone just followed suit as that was the standard.
Nowadays, 30% is just ridiculous.
I'm not sure why 30% is ridiculous. It might be, but I don't really see a good argument on how much is not ridiculous.
For example, Windows is a free for all platform. Anyone can run their own digital store front without restriction. However, even so, most digital store fronts are still going on 25% ~ 30%. Epic Games' own store is the major exception at 12%, but it's not exactly flourishing. Epic Games even paid a lot money for some high profile time limited exclusives, but apparently it's not very helpful.
Some might say, hey, that's because Steam is a monopoly! But at least for now I'm not aware of anything Valve is doing to unfairly keeping it that way (such as if you want to list on Steam you can't list elsewhere or something like that). Apparently gamers like Steam, and game developers are willing to pay Steam up to 30% for the benefit of being on Steam (IIRC Steam gives a discount for games selling over a certain amount, like US$10 million or something). Also note that there's nothing preventing gamers to install Epic Game Store along with Steam. I believe many do (at least I do). Yet people still prefer to buy games on Steam.
Furthermore, if you look at what Steam is doing, it's actually not that simple. It takes care of the money, which in the US can be up to 3% ~ 5%, depending on which provider you use. It also hosts your games, which is also a cost if you have to do it by yourself. It also has a forum, a customer relationship management system, cloud saves, multiplayer support system, etc. These all cost money, and if you want it to be reliable, can be a lot money.
Now, of course on iOS, it's not a free for all system. However, based on the experiment Epic Games did on Android, where they provide their own app distribution system to avoid the Google Play fee, ended up in failure (as they finally decided to list on Google Play), apparently it's not going to work. They are also allowed to run their own store on Android, which they are planning to do, but apparently not very successful (again).
From all these I think even if Apple allows Epic to run their own store to compete, they are not going to be very successful (as proved by their Android experiment). If Apple allows other companies to set up similar app stores, it's probably going to be all 30%, just like what happens to all these game stores on Windows. So, in the end, I'm not convinced by this "30% is too much" argument, and the strategy Epic Games did is obviously not the best way to present their case.
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