The fees to the retailer are nothing new, and AMEX is one of the, if not the, highest, which is the reason why many retailers will take Visa/Mastercard only, and why a smaller shop or sole proprietor has typically been willing to accede to a cash discount.
The Dodd-Frank legislation is really putting the squeeze on enterprises doing business by credit card, in more ways than new credit card regulation, so I'm not surprised they're passing it on to the public, directly. It is a bit Orwellian, however, to label the new practice a "cash discount" when it's nothing of the sort; it's the regular amount for cash and a higher sum if one is paying by credit card. It's going to be more difficult, I think, to get a real cash discount going forward.