Other news on this has quotes from Tim Cook saying that they'd have to find a way to track purchases on IOS and bill developers so that Apple still gets their cut when using other payment processors. For me, this is way over the line. If they want to charge developers to be on their store, fine. I don't have a problem with that. And charging for using them as a payment processor makes sense. Charging for using Apple…
Unfortunately, Apple has to maintain this rule because otherwise developers will implement workarounds to avoid charging in the App Store altogether. Remember when eBay charged a commission on the sale price but not shipping? Suddenly $50 items became $1 with $49 shipping -- so eBay had to charge the commission on the shipping too even though it didn't seem "fair". Same here -- every app would turn free, and charge t…
This is trivial to deal with. Apple already has rules on apps, they could go from banning fremium apps, to disallowing apps without a substantial free version to enforcing a reporting API on payments.
What they can't do is use their position in one market to force marketshare in another market (payment processors). That's classic anticompetitive behaviour.
(Aside, freemium apps have a low reputation, and that's why other stores without that rule aren't overrun with such apps)