Not sure whether this seems a valid question.Suppose someone has posted a question and i am also very interested in knowing the answer of that question. WHy cant we have a feature which says "notify me when someone answers" and if wanted we can be notified through email..
The "favourite questions" thing had, for a brief period, notifications on changes. It was shortly removed, and has shown no signs of coming back in the four years since.
See Jeff Atwood's post.