> "I cannot believe that Visa transaction overhead would be higher than Amex - there's something going on behind the scenes here."
Especially considering that card transaction fees (in the EU and UK) are capped by the Interchange Fee Regulation (IFR) [1]
But I suppose Amazon processes card payments in such huge volumes that they expect to get rates below the cap limits (0.2% for debit cards and 0.3% for credit cards), or Visa are applying excessive additional fees outside of the interchange fee?