In the video "Competition is for Losers with Peter Thiel", Peter Thiel discusses this. The problem here is in how you define "monopoly". If you're a large company, you want to say that the market is a lot larger than what you are operating in. To take this to an extreme, you could say that you're a technology company and if people dont like cell phones, they can use tablets/laptops/desktops. Conversly, if you narrow the definition of monopoly, there are tons of them. E.g. how many supermarkets are there within a 4 block radius of my house?

Because of this, instead of simply looking at scope, a common method is to look at what sort of behavior is the company taking. Is the supermarket lowering its prices below profitable to not allow another supermarket to survive in my neighborhood? In the case of Apple, I think people see the behavior of controlling the App Market as a monopolistic behavior which prevents others from competing.