A U.S. federal judge on Friday grilled Apple chief executive Tim Cook over whether the iPhone maker's App Store profits from developers such as "Fortnite" maker Epic Games are justified and whether Apple faces any real competitive pressure to change its ways. Cook testified for more than two hours in Oakland, California, as the closing witness in Apple's defense against Epic's charges that the iPhone maker's App Store controls and commissions have created a monopoly that Apple illegally abuses. App makers including music service Spotify Technology, European regulators and U.S. politicians who question whether the company that once urged the world to 'think different' has now become too big and too powerful.