Marica- it isn't (currently) on all of the forums because most people who visit the rest of the forums are members who contribute (or at least visit) frequently. The thought is that they will see that their thread/post has replies as soon as they go to the homepage. On the other hand, often the members who ask their question on the "ask a question" forum are brand new, and are likely to never remember to come back- so we email them to let them know that their question has been answered.
That's not to say we won't change things...only to answer the "why" behind how things are now
