You can draw an analogy with different educational media. There's a naive view of teaching that's surprisingly popular among 'thought leaders' like Thomas Friedman (and yes, I do have to use quotes whenever I use the phrase 'thought leader'). It reduces instruction to the words and pictures presented to the students. This is analogous to the idea that you could build a completely autonomous plane just by recording everything a pilot did on one flight then attaching servomotors to the controls and having them replicate all of the actions.
Good teaching is always an interactive process, though the interactions may not always be readily apparent to the casual observer. Even when you aren't actively answering questions or soliciting feedback, being an effective instructor means constantly reading your audience. You have to be alert to expressions and body language. If you see nodding and looks of relief, you might want to speed up. If you see wide eyes and slack faces, you probably need to slow down, add a simpler example, or even go back and start the lesson over..
After you do teach for a while, you will find that when you do ask questions or open up the floor, you will already have a remarkably good idea of where the kids are having problems.
If you take away that feedback channel, things become radically different, almost always for the worse. Explanations that seemed perfectly clear to the class in person will seem incomprehensible when presented over a YouTube video. Lessons that worked beautifully in the classroom will leave students confused and angry if done online.
This all ties closely to the concept of bookable instruction, classroom lessons that lends themselves to adaptation to books and other non-interactive media. Most history lessons are fairly bookable; almost no math lessons are.
When it comes to educational technology, the medium is very much a part of the message. Unfortunately, it’s a part that has been all but completely lost amid all of the hype over MOOCs and iPads.