If I understand correctly, the difference is that apple owns both the store and the payment processor, and require exclusive use of the payment processor (with associated uncompetitive fees) to gain access to the store. This would be somewhat akin to Wells Fargo also being in the business selling porn while not processing payments for anyone else who competes with their product. In the current climate, it seems unlikely a judge would rule against apple for anticompetitive behavior, but there are several reasonable cases to be made that this is anticompetitive and even anticonsumer.