I am not suprised that Amex foreign currency charges, stated as "the rate" plus 2% are higher than Visa charges with the same stated mark-up. I've found Amex effective rates almost always higher and I thus try to never use Amex overseas.

As for overseas costs of business being higher, I don't know about that but I do know of no reason why Amex' cost of overseas business should be higher than Visa's cost of overseas business. In fact, in many places Amex isn't accepted at all in mid-level stores and restaurants, but only at the higher end ones. Thus I'd think their costs would be less.

Mileage Plus Visa and MCs have only the 1% mark-up from Visa/ MC- First USA does not add anything to that. And they start from excellant rates, so I find I get a very good net rate from them.