It is likely extremely difficult to win such a suit based on challenging the terms of an agreement that you agreed to repeatedly. Every single change to the TOS for a developer account requires acceptance. I doubt there is any part of this agreement that Apple did not write with this exact circumstance in mind. No matter what Epic challenges based on this argument in the end they will give in and look like fools. Maybe if they are lucky Apple will lower the % by a little. This is not cutting edge law here.
I'm not sure why you feel qualified to comment on the legal aspects on this case based on just a primitive understanding of offer and acceptance (which isn't the point of contention here). You can't have an enforceable contractual term that is illegal, even if both parties have agreed to it. The legal issue is whether Apple's ToS contravenes some aspect of competition law.
IANAL but my understanding of antitrust cases is that voluntary consent to a EULA is indeed a relevant factor in determining market power for antitrust claims. See the discussion in Blizzard Entertainment Inc. v. Ceiling Fan Software LLC:
> Blizzard raises this argument in its motion, contending that Defendants cannot establish antitrust claims based on its users' voluntary consent to the EULA and TOU. (Mot. Br. 22–23.) Although Blizzard does not argue this point in the market power analysis, the Court finds that this discussion is applicable to whether the market power requirement is established. Blizzard cites Newcal, Queen City Pizza, Inc. v. Domino's Pizza, Inc., 124 F.3d 430, 441 (3d Cir.1997), and Apple Inc. v. Psystar Corp., 586 F.Supp.2d 1190, 1201 (N.D.Cal.2008), to show that Defendants cannot base its claims on the aftermarket restrictions. ( See Opp'n Br. 17.) These cases explain that the law prohibits an antitrust claimant from asserting an antitrust claim “resting on market power that arises solely from contractual rights that customers knowingly and voluntarily gave to the defendant” when they purchased the initial tying product.
If I give you a contract stating that you allow me to shoot you in the head, you sign it, and I pull the trigger, I still go to prison for murder. Whether or not you "agreed" to something is irrelevant if the contract cannot be legally enforced, which is what Epic is hoping to prove with this lawsuit.
However, the contract is the only thing which allows Epic to publish in the store. So it is not enough for them to simply get terms they don't like to be declared illegal, they still would have to get the terms they like into the contract.
If Apple changed their stance to "all services and digital goods associated with your app must included in the original purchase price", that might meet the court's requirements for legality but it would leave Epic without their current revenue stream.
