My merchant services account is with BoA. When we process a credit card, the rate (discount) we pay varies by not only card type (Visa, MC, Amex, Discover) but also by sub-type (debit, credit, reward, etc). A Visa/MC reward type card we may pay as high as 3% discount.
So, these 2% reward cards seem to be getting a big chunk of the discount I pay. Not sure if everyone pays the same, but when I look at our discount schedule for merchant services, the list and rates is pretty big and extensive and categorizes card type fairly specifically with rates varying among those types.