I am pretty sure that people rarely step through video to select individual frames to post on the internet. There are exceptions, especially with regard to evidence of crimes and women without underwear. But here's what I know: When you record a human being in motion, at thirty frames per second, you capture hilarious in-between expressions and postures that you'd never notice while watching them in motion. Some people are "worse" at this than others. When I worked on video capture, I watched many talking heads. Some of their faces remained quiet and placid while they talked; others flitted through hilarious momentary expressions that you could only see by looking at individual frames. Based on my experience, I have to wonder why such expressions are not showing up all over the internet. But I think I know why:
Good hi-res still shots always set the standard, at any time, for quality images on the internet. Still-frames are generally much clearer than motion frames. In fact, most people record their video in compressed formats. If you step through compressed formats of people in motion, you'll often see little detail, blurred images that trick your eye into seeing smooth motion. But these frames are no where as clear as posed still shots. Some day the quality of motion frames will dramatically improve, and then you'll all get to see these hilarious expressions. I doubt we'll have to wait more than ten years, so let's hope for the best!