Catching up with some older mail of mine, I got a letter from Amex last month that says:
This letter only seems to apply to my Gold Credit Card Amex. I didn't get a similar letter for my Plat Credit Card Amex.
Effective 9 July 2010, we will no longer refund the Conversion Commission for purchases made in a foreign currency when the goods or services are returned. Please note that we do not charge an additional Conversion Commission on returned purchases.
This letter only seems to apply to my Gold Credit Card Amex. I didn't get a similar letter for my Plat Credit Card Amex.