They don't offer fraud protection, but still track and deal with fraud on their own network. They have to deal with international laws. They can and will decline transactions or cancel cards. They keep track of how merchants are being used.

A company I've worked for has the letters to prove it. You do not want to get a certified mail envelope from MasterCard (not a merchant or bank, MasterCard) containing a letter with a short deadline.

Needless to say, shit got fixed. Quickly.