What is EUR to USD conversion rate at bitstamp?
I believe the EUR / USD conversions are preformed by the bank with which Bitstamp works. They have conversion rates which don't appear to be market-driven, but are set to a fixed rate that includes the bank's fees.

The exchange rates link provided on the website leads here:
http://www.raiffeisen.si/pripomocki/menjalniski-tecaj/