And apples taste like oranges, am I right? No, addons can't steal passwords. Back in the day it was possible, through somewhat hacky methods, to "skin" the login page. There was a little "addon" that remembered the login credentials for you (or at least the login name, don't recall now). Once Blizzard found out they fixed that hole pretty quickly since it could and would have been used for malicious purposes.
So before you try to come with "insightful" comments, make sure your facts are straight. An addon is not a keylogger and a keylogger is not an addon. Some people try to spread keyloggers using fake or others addons, but that's unrelated to the addons themselves.