Gonzalez said the profits Apple reaps from game developers "appear to be disproportionate." "I understand this notion that somehow Apple is bringing the customer to the dance," she said. "But after that first time, after that first interaction, the developers are keeping customers with the game. Apple is just profiting from that, it seems me." Cook disagreed. "The free apps bring a lot to the table. Only the people who are really profiting in a major way are paying 30" percent commissions, he said. Epic has tried to show that Apple's iPhone is a lucrative platform that locks in users, pointing to an internal Apple document that Epic alleges showed the App Store had 78 percent operating margins. Cook said the document did not reflect the full costs of running the App Store.