John,
I think there is a problem or lack of agreement. When you state,
"Here's how I've been doing it lo these many years: If there is a canned video on the subject that is better than anything I could do myself without huge effort, I just show the video ... but I'm still there. If anybody has a question, or if the video says something I want to emphasize or disagree with, I can pause the video and deal with it. We can discuss everything afterwards."
That isn't as truly possible with a mooc. As a massive online course, students will be watching the video at different times. If you have a class of 50, 500, or 5,000 students online, you can't really pause the video at the point where they have a question. You can anticipate where they might have a question and clip the video, or you could insert your commentary with an adapted movie. The statement that the mooc instructor not being as available is due (as I understand it) to the fact that the instructor isn't there, and has so many students that they can't talk / interact with all of the students.
Perhaps I misunderstood something.
Paul Lulai
Physics Teacher
St Anthony Village S.H.
3303 33rd Ave NE
St Anthony Village, MN 55418