That's bad practice by the CC company. :/ If you get a Visa or Mastercard CC issued by your bank, I think they have to follow the Visa/MC official exchange rates in all cases. Have you checked?
That's how it works with my CC, anyway. They don't charge me extra for e-shopping in USD either. Is that common practice with UK CC companies and banks?
If I recall correctly, ED shop prices (after Visa currency conversion) are cheaper than the Steam eurozone prices.
As long as you don't have a cutthroat CC company, I guess.