If you go to the main message board page and look at a thread, you can see all the posts. If you look at an individual post and there is one under it that is indented, that means someone replied to that post correctly (using the tutorial method).
If you use the quick reply button, there is no indent and it just says RE: (title of post). There is no way to tell who that person is replying to.
All in all, DS has toyed with the idea of getting rid of the "threaded view" because, my guess is Yuku is giving him trouble (sorry to speak on your behalf, DS). Most posters do not want to get rid of it because then SPS basically turns into a smaller version of TigerDroppings. I don't want that.