Message Boards and IMs aren't on the list because while FB or Twitter are a single entity, IMs or Boards are amde up of dozens or thousands (respectively) different sites.
From the point of view of a TechAdmin I disagree with you on the question of boards. Like Facebook or twitter, a board is a fixed website where people from all over the globe can make an entry. Basically, there's no difference between a facebook or twitter page and a thread on a board:
Someone says something and others reply to it. The whole discussion is displeyed on one single page. Many of such conversations are going on simultaneousely on the very same website.
Technically it's precisely the same.
Particularly in the lounges on this board which are restricted only to members of a certain rank there is far more social interaction going on than on many social media. I can only speak for myself but in teh course of the last 12years I have met quite a number of people on message boards who have become my real life friends. If you have a look at my profile and the friends list there, about 3/4 of the listed persons are RL friends of me. My old buddies Santaman and Jim Gamma are closer to me than my genetical brother.
I believe most of us oldtimers ahve made similar experiences.
Chats usually come as a secondary level: you meet people on a board, PM with them, exchange emails, meet on instant messengers or in chatrooms, then you meet in real life.
I don't think that more than 5% meet for the first time in chats or on instant messengers.
The online social life parallels the real one:
IRL you meet people at concerts, in movies or at museums etc. - in short, at places of a common interest. You get into a conversation, find you like them, you continue by meeting in a pub or cafe, exchanging phone numbers and perhaps finally developing a friendship.
Getting to know a person by a telephone call (the equivalent to an IM) is rare, though I know of a case where someone who dialled the wrong number made friends with the person he called accidentially.