That equivalence is awful. What is the profit margin of airlines vs the app store? There is a real cost to an airline seat, and there is a real cost to publishing an app on an app store (and all that it entails). The difference here is that airlines have tons of competition driving down margins, while no one is allowed to compete with Apple for iOS customers.
The existence of large profit margins is not prima facie indication of a lack of competition. Apple makes a huge profit margin on iPhones but I don't think there's anyone who suggests that the smartphone market is uncompetitive. To that extent, the first part of your point doesn't really hold up.
On your second part: one of the defining qualities of a retail store experience is, in my experience, that no-one is allowed to compete with the owner of the store. No-one would say it is uncompetitive that the owner of a supermarket doesn't allow you to put your own goods on their shelves.
Presumably your point is really that Apple's App Store is such a large fraction of the total smartphone app market that it has, and uses, monopoly pricing power in abusive way. That's a more interesting point.
The fact that's interesting to me is that, as far as I know, since Apple created the App Store, it has always charged 30% (modulo the recent small business program); from the very beginning when the market was practically non-existent, with no guarantee of success, up until today. So despite the fact the market has grown from nothing, Apple hasn't sought to increase their fees.
Also, look at comparison points. If you look at PC video games, those can often be bought in physical form, downloaded direct from their publishers, etc. etc. I mean to say there is no restriction on alternative sales channels. Nonetheless, a huge number of game developers choose to sell on Steam; where, coincidentally, the store cut is also 30%. They complain about it, but they do it.
