The rules for hand-holding lenses was always based on the object in the shot not appearing blurred when printed FULL FRAME. Almost nobody every blew up 35 mm negatives to anything approaching what we do every time we zoom in past the pixel-level detail on our shots. To not have motion blur on something 4 microns across (instead of 20 mm) you'd have to have a shutter time 5,000 times faster to have the same effective blur vs. size! Honestly, I'm surprised it hasn't been more of an issue to-date. The only thing saving the discussion until now is the fact that most lenses have a point spread function that spans multiple pixels. However, the best lenses can be sharp enough to resolve down to the pixel level now.