" (Going further, many charge cards offer cash back on each purchase — they can do this because the cash-back percentage refunded to the customer is less than the transaction processing fee paid by the retailer.)
So the same-price rule is good for the user, and good for Apple."
This type of arrangement is not good for users and is very anti-competitive.
Banks often offer reward points worth 1% of a purchase in exchange for the use of their credit cards which incurs something like a 3% fee on merchants. The merchants have to increase their prices to maintain their margins but since they are contractually obligated not to charge credit card users more, price is increased for everyone. Even those who avoid credit cards end up paying the banks for other's use of them. If fact those who use the cards pay a little less for than those who don't because they get the 1% kickback. Next time you spend $500 of airmiles or reward points, know that you imposed $1500 worth of fees on customers likely not even using the service. The bank gave you a $500 kickback and pocketed $1000.
This scheme basically amounts to imposing a tax on everyone and it's enabled by the one percent reward points along with the price matching rule.
It's the same situation when selling on iOS. In order to pay for Apple's fees and maintain competitive margins, merchants will have to increase the prices of their products across the board, even when they are sold completely outside the Apple ecosystem. This means that if Amazon keeps their Kindle app in iOS, Amazon will have to increase prices _on every devices_ and when someone purchases a book on an Amazon device, through Amazon only, they will be indirectly paying a portion of the sale to Apple. That, IMO, is screwed up. This type of rule is illegal in many countries (at least with regards to credit cards) because it is clearly anti-competitive.