Well since he was driving a Manual his hand would need to be on the shifter to have more control. I rarely have both hands on my wheel, my other is always on the shifter, where his was.
I also only remove my right hand from the wheel when I am shifting, and immediately return it to the 3:00 position. Aside from having less wheel control, I don't want to be putting any inadvertent pressure against the shifter, slowly grinding up any transmission parts.
I have plenty of control with my one hand even on rough roads. Also I don't put pressure on my gear shifter but I find it less distracting to just leave my hand there than to keep moving it back and forth.
I usually shift down going in, then shift up coming out so it would be pointless to move my hand. In any case I have more than enough control. I've not lost the wheel on a turn yet and been driving like that for 9 years.
