The most obvious difference between Visa/MasterCard and Amex and Discover is that with Amex and Discover, there is a single entity that is both the merchant bank for all merchants and the card issuer for all cardholders. There is no independent association. So, in this situation, every dollar that Amex would refund to a cardholder comes directly out of their own pocket, and the entity that makes that decision is the same person that would have to pay out the refund.

This is very different from how Visa and MasterCard operate. For those types of cards, the cardholder's bank and the merhcant's bank are usually different. So, if you call the bank that issued your Visa or MasterCard and request a refund in this situation, they're likely to be helpful, as they get the money back from whatever bank was handling National's business. Plus, National's bank must comply with the refund in this situation, as they must comply with the rules of the MasterCard International and Visa International associations if they want to remain in the credit card business. The associations are much more concerned about maintaining the integrity of the brand image than in an individual situation like National's. This is helped by the fact that the entity enforcing the rules doesn't actually have to pay out the money, so there's no conflict of interest like there may be in other situations.

As for the claim that Amex doesn't need to pay because most of their cards are charge cards as opposed to credit cards, I disagree with this interpretation. While it's true that many of their cards are called "charge cards," the fact is that they are still extending credit to the customer, although only for 30-60 days instead of on a revolving basis. But, it's credit nonetheless, and therefore would fall under the terms of any federal consumer credit protection laws.

The people that might end up hosed are the people that used debit cards from their credit account. Even though they may have MasterCard/Visa logos, no credit was involved since the money was withdrawn directly from a deposit account.