If video has inexact focus you can notice it. (Though people will still use those shots in theatres.)
On Hollywood productions, there's a focus puller whose job it is to handle focus (and some other camera department duties).
Shooting everything at a higher frame rate wouldn't affect focus. Perhaps you're talking about motion blur???
You misunderstand... and didn't really read my post I guess. Or maybe I wasn't clear. So I will repeat. There are 2 big problems with taking stills from videos.
FOCUS: On a frame to frame basis, any scene with some tracking motion going on is going to have several frames (or perhaps most) somewhat out of focus as the focus puller makes his adjustments, even though as a whole the key part of the scene appears in focus. Sum of the parts. Our brain ignores these spurious defects because there is movement going on and completes the image mentally. Persistence of vision etc
But if you pull one of those frames out and turn it into a still photograph - then we notice it, just like we notice problems with focus and blur in any other still. It's distracting. It's unusable for anything beyond documentary purposes.
It's simple to see this, just go do a frame grab on a movie scene involving tracking. And of course, the higher the resolution of the frame, the worse it appears.
SHUTTER: Most scenes are shot around 1/24th to 1/30th of a second per frame. Different effects and situations might have faster speeds, but its still really quite slow, compared to what stills photographers trying to capture motion are used to.
Therefore, there is motion blur in each frame. Again, our persistence of vision puts them all together so it appears alright. But again, if you pull out a still - your main actor is going to have a mushy face or something else.
Like I said, this is why movies have a stills photographer on the crew I don't see that changing any time soon.