I can understand if people don’t want the option panel to be overloaded. However I think the default behavior (and maybe only one) should be to show notifications, not activity.
Personally I find it really stressful to have a number in the page title suggesting someone is contacting me when no one is. I have never ever seen this current behavior in any other software and I don’t know what it is good for. It doesn’t even display the number of unread posts but the number of unread posts since you last loaded the page. When is that useful to know?
In my opinion this is a bug.