I think most people are mixing things up here. The issue is not if Apple is a monopoly or not. The issue is if they are abusing or not of their dominant position. They are. A 30% cut on apps sold in the app store is high but acceptable. BTW, Epic charges 12% on their games store. What is completely unacceptable is the cut they take on in-app purchases and subscriptions. It's like if a truck manufacturer sells you a truck and then wants 30% on every fee you collect by transporting stuff. It's not related to apple's role in the purchase, it's an abuse that apple can do because they have a dominant position.
An additional problem, which is related, is that apple also competes with their own services. Apple music gets the full 10 dollars a month from every user, they don't have to pay the 30% fee. Apple imposes absurd rules for xCloud and Stadia (they would have to approve any single game) effectively keeping them out of the apple ecosystem because they want to protect their own gaming services. This is an abuse of dominant position as well and it's unfair competition
One similarity are bank and credit cards. What if Mastercard starts charging a 30% fee on everything that you buy?
"A manufacturer’s own products do not themselves comprise a relevant market."
"A company does not violate the Sherman Act by virtue of the natural monopoly it holds over its own products."
These are direct quotes from case law… the precedent has been set and upheld by:
-Parsons v Ford 1982.
-Spectrofuge v Beckman Instruments 1978.
-TV Communications Network v Turner Network 1992.
-Belfore v New York Times Co 1986.
-Carlock v Pillsbury Co. 1989.
-Elliott v United Center 1996.
Among others.
Elliott v United Center is a really good one here. About the United Center's policy on food sales within the United Center and a peanut vendor being angry he couldn't sell peanuts outside the UC and have patrons enter the facility with them...
The serious point here is that the United Center is certainly a popular facility in Chicago. It serves, over the course of a year, millions of customers, and it is undoubtedly a prime spot for vendors of all kinds to ply their wares. But this implies that the relevant market should be expanded to all other comparable places in the Chicago area. Absent collusion, even if each stadium or arena had a policy similar to the United Center’s policy, there would be no violation of the antitrust laws. In such an expanded market, furthermore, it is very doubtful that the United Center has any significant market power. And we have explicitly rejected the proposition that a firm can be said to have monopoly power in its own product, absent proof that the product itself has no economic substitutes. See Digital Equip. Corp. v. Uniq Digital Technologies, Inc., 73 F.3d 756, 761 (7th Cir.1996); see also Bendix Corp. v. Balax, Inc., 471 F.2d 149, 160-61 (7th Cir.1972).
Can't have a monopoly within its own product... check.
Absent proof the product has no substitutes... well, they aren't even remotely close to the dominant product in this market.