Antitrust competition is not measured primarily by marketshare but market power, of which the main measure is pricing power, the propensity of people to shift from one offering to another of prices change. With regard to the App Store, would the people — app sellers — whom Apple charges for the service start to move to an alternative if Apple increased prices even incrementally, either expressly in terms of dollars charged or effectively by more-expensive-to-comply-with other terms?
No? Looks a lot like a monopoly, in antitrust terms, then.
What are effectively independent, descriptively similar, side-by-side markets that people don't move between in response to pricing changes aren't the same market for antitrust purpose, even if conventional media coverage labels them the same market and talks about marketshare in the combined market.
