In reply to Philip Cohen.

"there is no good reason, from the consumers' point of view, for the merchant to get anything out of the transaction other than the funds in their bank account the following day"

Why not? I bet Starbucks has proven you are wrong. There may not be any momentary savings - MCX will disagree with you - but what about discounts, loyalty and rewards. That only a merchant can give the consumer at the checkout.