The way you define the market is by considering whether there are viable substitutes.
For example, two parking garages across the street from each other are strong substitutes. You can easily pick either one based on e.g. which has the best price. But a parking garage in New York and a parking garage in Boston aren't in the same market, because you can't reasonably park your car in New York and get out and walk to your destination in Boston.
You can easily have viable substitutes for app distribution on any given platform. Windows has a first party store but you can also install apps with Steam or download them from the developer's website. The Windows store and Steam are in the same market, so neither of them has a monopoly on distributing Windows apps. The same as two parking garages across the street from each other, or a Walmart and Target in the same mall.
If the operating system prevents competing app distribution methods, there is no longer any viable substitute for the official one. This is what the OEM wanted, right? No competition for their app store -- no substitutes, a monopoly. But then that's just what it is. You don't have to monopolize markets ancillary to your primary one, but if you do, you have.
I would say that Android is a viable substitute for Apple and vice versa when it comes to phones though. So I think there actually is a viable substitute. Customers can absolutely choose the one they want. But again if you redefine the market to Apps you can install on IOS then certainly that's a monopoly. I just question if that's a reasonable way to define the market.
> I would say that Android is a viable substitute for Apple and vice versa when it comes to phones though. So I think there actually is a viable substitute.
We're talking about the market for app stores, not the market for phones.
> But again if you redefine the market to Apps you can install on IOS then certainly that's a monopoly. I just question if that's a reasonable way to define the market.
But why? You haven't provided any reasoning.
Apple's store and Google Play aren't in the same market because they aren't substitutes -- you can only use one or the other depending on which type of device you want to install the app on. That isn't a law of nature -- Apple could offer Android apps in their store and stop preventing Google Play from distributing iOS apps. But they don't, and because of that they're not in the same market.
For example, two parking garages across the street from each other are strong substitutes. You can easily pick either one based on e.g. which has the best price. But a parking garage in New York and a parking garage in Boston aren't in the same market, because you can't reasonably park your car in New York and get out and walk to your destination in Boston.
You can easily have viable substitutes for app distribution on any given platform. Windows has a first party store but you can also install apps with Steam or download them from the developer's website. The Windows store and Steam are in the same market, so neither of them has a monopoly on distributing Windows apps. The same as two parking garages across the street from each other, or a Walmart and Target in the same mall.
If the operating system prevents competing app distribution methods, there is no longer any viable substitute for the official one. This is what the OEM wanted, right? No competition for their app store -- no substitutes, a monopoly. But then that's just what it is. You don't have to monopolize markets ancillary to your primary one, but if you do, you have.