Did you compare the exchange rate that the merchant applied in making the conversion to US Dollars versus what you expected the credit card company would use? My understanding is that the rates are typically unfavorable -PLUS- your credit card company may still charge a fee for a foreign transaction even if denominated in dollars.

This is exactly the situation referred to in the article above:

"Using the wrong card can add close to 10 percent to the overall cost of a given purchase," she said. "For example, your bank might charge you 3 percent for a purchase, and the merchant might charge 6 percent to convert the charge to dollars."