Hi Doug - I agree that this is of critical importance: Whether or not the facilitators are engaged with students by answering their posting has more of an effect on the sense of community.
I'm also with you regarding the importance of the group's sensitivity in eliciting responses from those who may not be expressing their ideas. Silence may be correlated with lack of trust.
Good to hear that you can still feel part of the community even with limited synchronous interaction - following along with the story and thinking my answers to the questions almost sounds like how we can be intellectually/emotionally drawn into television game show even though it has been prerecorded.
Appreciate the Open University link - lots to explore there :)