Fair point. I admit that Khan does an incredible job. I believe it [lecturing to a microphone] is an extremely rare and underdeveloped skill. "EVERY" might have been hyperbole.

But when the lecturers at hand are professors who have spent decades teaching to a room full of students who become visibly impatient, confused, eager, or antsy --- they should keep doing that.

To keep a pleasant rhythm to instruction, many professors tell jokes; I think it's VERY hard to tell a joke to a webcam when you are used to an audience.