defining the relevant market is very frequently, if not nearly always, the most important question in an antitrust / unfair competition lawsuit. As your example points out.

> The fact is that there are alternatives (for both consumers and developers) to the iOS app store. They don't get products from or on iOS, but they can still buy and sell comparable products.

But that's usually always true: 90s era Windows users had alternatives in the Macintosh and Sun workstations, and Monopoly-era AT&T users had alternatives in CB radios, etc.

That explainer you linked even uses language that excludes some competitor products: "Microsoft was found to have a monopoly over operating systems software for IBM-compatible personal computers" [emphasis mine].

That is a fair statement, but as far as the FTC is concerned that's probably not enough....

> By the reasoning of your stament [sic], all that's needed to establish a 100% monopoly is a sufficiently narrow definition of market.

I don't think the reasoning in my statement is sufficient to identify a monopoly, and it wasn't indented to be such. What I was trying to communicate is that you can't disprove a monopoly based on comparing marketshare numbers, and the actual determination is probably rather complicated and requires a lot of expert judgement.

I think Apple's business practices warrant careful and continuous antitrust scrutiny. If they're a monopoly, the form that takes will probably be significantly different than the one taken by 90s-era Microsoft.

There were alternatives to Windows on IBM-compatible PCs, but MS actively worked to block them in the marketplace. MS also actively worked to block competitors who would break platform-centric software via things like (as Netscape was after) creating a platform-agnostic software delivery platform.

It's also important to note that the FTC doesn't actually care about monopolies in all cases. They care about monopolies that arise from abuse and anti-competitive behavior or that are used to abuse consumers and competitors.

Show that Apple is in a monopoly position (as a player in the mobile hardware/software business space) and that they got there by way of anti-competitive behavior. Or that they've abused this position to artificially control pricing and other things. That's what needs to happen to establish an anti-trust case against them.