Anti-competitive behavior doesn't require a monopoly. There's collusion/price fixing, libel, and other ways to interfere in a business which are all illegal without having a monopoly.

If we use cars as an analogy, we require car manufacturers to allow service by other mechanics, but we don't require the same for phones (yet). Car manufacturers do not have monopolies.

At some point, asking, "Does Apple have a monopoly?" becomes the wrong question to ask.

>> we require car manufacturers to allow service by other mechanics

True, but that required a new law, and sure a new law could also be deployed with regards to Apple.

I think it requires having a dominant position, which in the in app purchase market is pretty much the case (by revenues).

Lots of android in the market but sold to people who couldn't tell the difference with iOS and wouldn't even know how to buy an app.

I think anti-trust also requires a non-privately administered market. In Apple's App Store, they own the servers serving the app market, giving them control.

I don't think the government could force them to keep an app on their server and continue to serve it to consumers running their software if they didn't want to.

Actually, in terms of total revenue both markets are pretty close together now due to the larger install base on Android and ever increasing monetization of users.