Question regarding Scam hacks : World of Warcraft General Discussions

I was logged on the other day and read that a few of my guildies had gotten their accounts hacked via keylogging. You know that a keylogger is entirely what it is... making a complete logs of keys pressed (correct me otherwise) and if you only enter your password and not the username then the scammer is S### out of luck. There is the option that the wow.exe can remember your username making it easier to the user by not having to enter in your username every single time. Is this a good safety prevention measure or can the hacker dig up the username too?