But it's manifestly not just a transaction fee, it pays for the curation of the store, server storage space, bandwidth, royalty payments for patents which Apple

But it's manifestly not just a transaction fee, it pays for the curation of the store, server storage space, bandwidth, royalty payments for patents which Apple have been shaken-down for, advertising on the Apple website, and finally the actual fee to MasterCard/Visa is all covered in that. It's a store, that's what stores do, provide some value-added and charge a markup.