What about transactions that weren't made directly with a credit card, but rather with an Apple Store gift card purchased from a physical retailer? Possibly during a 20% off sale? Even if you elide any such discounting, Apple's transactional cost is going to be far, far higher than 5%.

I doubt there's any publicly available hard data around the costs of running the gift card ecosystem, but a number between 15 and 35 percent would not surprise me at all.