They also might be linking your cd-key to your login.. meaning you can only login to the account that used the cd-key you installed the game with..
I'm a little confused...isn't this how it works now? ?( I mean..we do all have 2-5 additional CD keys tied to 2-5 different usernames... right??

I've run into several people who think we play 5 toons from the same account/login.