Take Netflix for example, which doesn't run on Apple's distribution network... Should Apple have to pay for part of the deployment of all the assets and feeds? They don't... the margins are already thin and Apple frankly doesn't deserve 30% of that recurring revenue.
I think if anything this kind of thing makes the case for explicitly having multiple tracks— maybe an enterprise one where you pay a 5-7 figure fixed annual fee (for support, timely review, policing of the store for phishing/knockoff apps that target your own, ensuring a direct hit for explicit searches) and then either a single-digit percentage of revenue or for free "portal" apps, some other way that Apple is compensated for user engagement. And then a totally separate indie track where all the revenue is yours up to X, after which some kind of sliding scale kicks in.
In reality, there are almost certainly enterprise deals going on behind the scenes (or at least mostly behind the scenes, cough Epic) and the details of those are almost certainly very proprietary, due to how the negotiations would occur. But having at least one option for which the details are public would be nice.
If they were serious about it as a revenue stream, it would make sense to go with something more like the UE4 model, where it's free up until the point where you're a big fish, and then a more aggressive fixed fee kicks in.