THe lack of dual spec does not force people to go out of your small group; in fact, the lack of dual spec encourages people to stick to a small, consistent group. Likewise, having dual spec does not discourage people from going outside of their normal group of people to fill out a group; in fact, it encourages people to do so.
If me, and 2 of my friends are on, but our tank friend is on, then we're limited to only inviting tanks. If we can dual spec, then I can switch over to my tank spec, and the healer can switch to a dps spec, allowing us to invite a tank, healer or dps. That massively increases the pool of possible players we can invite.
The 2 parts of this statement dosn't really have anything to do with each other either. Even back in EQ1 it was common to get into a group and not chat a bit; certainly if you had a competent puller there wasn't time to for anyone to chat. Nor are all lfd groups in wow totally silent.
the issue is the content: if the game is paced so that the players have to take regular breaks, there will be chat, and if not there won't be. Whether the group is formed automatically or not is irrelevant.