Not knowing who is online and when is a sort of protection for you.
I find it annoying that even when I'm not logged into the forums it shows I'm online in the game.
If it shows someone is offline, you can just watch for patterns and figure out when they work or sleep and attack then. Granted, you can do that with growth patterns anyway, but it's a bit harder that way.
There are even people in EEK and WTF that I don't want to know when I am active or not because I don't trust anyone outside of my usual circle of friends. While I am secure in the knowledge that my army is bigger than my mouth (a huge achievement), it's still not a good idea to give them an idea on when I am most vulnerable.