It's not aiming to do away with spam all together, it's aim is to decrease the abounding threads that start over night and dwindle by the next, threads like "Showers!" and "Post Faster", which are not so much public threads for discussion as messages and conversations between two or three people, things that could easily just be carried out in a chatroom.
The threads where things are actually accomplished, plans and events, are obviously not the target here. Just the forum litter, so to speak.
Just think of it as text messages vs. emails, one is generally much more worth keeping than the other, because the other has a reputation for sporadic and impulsive thought.
*And you are misunderstanding the point of this topic, Miria. The point is to differentiate between spam and chat. The chat threads are, essentially, the problem because they are so abundant and only important for a moment, if at all. There is a difference between chat and spam, chat is like the lowest level of forum content, whereas spam is too minor to include in a post count, spam could be seen as even lower because it is just so...unnecessary and universally functionless (generally).