Since the other thread reached the limit on comments I'm starting this one.
On our btags, not everyone wants to get the message "Hey lets run mythics" right when they login or "Hey can you tank this" all the time.
Actually, you shouldn't NEED a reason as to why you want to appear offline to your friends. Maybe you just wanna solo stuff without being interrupted.
Inb4 "well why did you add them then!"
That's irrelevant, message services like Skype and Yahoo messenger have options to show as "offline" so asking for it to be implemented for WoW isn't uncommon. Thanks !