IANAL, but I think the strategy epic will use is called tying in anti-trust law. That means obtaining an unfair advantage for one line of business by requiring its use in another line of business. The android app market is big in numbers, even bigger than the number of iPhones, and therefore it may be difficult to call the App Store a monopoly. In Epic’s case, while the App Store may or may not be a monopoly, forcing anyone who uses the App Store to use Apple’s payment services as well may be the illegal part in the eyes of the court.