You're assuming "iOS" and "iOS apps" are the same market, which they aren't in the same way that LibreOffice is in the same market with Microsoft Office but not with Microsoft Windows.
The argument you could be trying to make is that Android apps and iOS apps, or Google Play and the iOS App Store, are the same market. But you can't install Android apps on iOS and you can't get iOS apps from Google Play.
And iOS app developers are the customers of the iOS App Store. They pay Apple for it and have no alternative. "Switch to Android" doesn't work because it is the device customer who would have to switch to Android, not the app developer. The app developer is already in both. It's like facing a retail monopoly in California and what you're saying is to go buy retail space in Texas. That's not the same market.
You are a monopoly when you have pricing power over some good or service (the ability, in some range, to raise prices without losing sales to a competitor). Having less than 50% share in some market using the market boundaries usually drawn by analysts does not prove or imply the absence of pricing power.
The good or service being "mobile phones" or "mobile apps" -- e.g. the whole market they belong to.
Not "iPhones" or "iOS apps".
Any company has "pricing power" over their own products and marketplace.
>Having less than 50% share in some market using the market boundaries usually drawn by analysts does not prove or imply the absence of pricing power.
No, it just makes it irrelevant as to the law.
No, it doesn't work that way. If you have pricing power on, say, iPhones -- you can raise the price and sales don't move to someone else -- you have a monopoly because price power demonstrates that whatever putative competitors exist are in a functionally separate market, not substitute products in the same market.
> Any company has "pricing power" over their own products and marketplace.
No, companies in competitive markets lose sales to competitors when they raise prices, which is exactly what pricing power means doesn't happen.
No, Microsoft was a monopoly on the OS market.
You cannot be a monopoly with < 50% share like iOS has (and it's not a monopoly to have 100% share on your OWN platform and dictate terms there, as long as your platform is not a monopoly on the overall market).
In other words, people and devs dissatisfied with how iOS does things, can always go to Android (or Windows Phone).
People couldn't do that when Windows had 95%+ of the desktop and enterprise market, because there was no escaping it.