I think the fundamental thing here is that this isn't merely a store. The Apple ecosystem is large enough to BE a market in itself.

It's not about the market for apps, or the market for smartphones. Those markets are comparable to any market.

This is about the market for apps ON the apple ecosystem. And the problem that is being solved is: Apple can't have a monopoly on that market, such that they can (for example) charge a commission for every sale.

Basically: we can't allow a company to be so successful that their STORE becomes a MARKET.