Some great (and some not so great) analysis of pros' mechanics in this thread, but as a non-pro who wish to emulate the zero-head movement stroke of a Cheng or Lombardo...where do you start?
I think it's somewhat irrelevant to point out the quirks among pros. Obviously they are not affecting their game, and obviously any movement they have is after contact with CB. In my own game, I feel many missed shots are the result of movement prior to contact, and so my goal is to establish a stance/stroke/etc that incorporates zero movement.
This is more difficult than a matter of mental will, "just staying down" on the shot. I can stay down on the shot until the CB stops rolling, but when I look at the tape I'm still lunging before/during/or after contact. When I'm "in stroke" all the movement occurs after contact; when I'm struggling it seems i'm moving during or even before contact. Therefore it makes sense to me that if you are to improve on your fundamentals, trying to work out a set of mechanics that allow you to comfortably stroke through the ball w/o ANY head movement is highly beneficial to anyone not currently playing at pro speed.
IMO, watching Hunter's game...when he misses a shot it seems like he mis-aimed or misjudged english/speed, rather than anything to do with his fundamentals. This might or might not be true for pros with pronounced head/shoulder movement, but my point is it's not obvious with those guys.