Why do we get notifications when on the questions page and a new question is added but we don't get notifications when somebody responds to a post of ours? I'm referring to notifications in the tab such as "(1)".
I guess you mean that the title doesn't change when new comments are added (whereas new questions cause a slight change in the title of the page).
Note that answers don't have an effect like that either. So comments, which are second-class citizens of the kingdom of StackExchange should not be expected to have that luxury either.
What is still true, though, is that you get comment updates in the page. So at least you don't have to refresh.