Yeah, if you're going to move your hands, it's important to move your whole arm and not bend at the wrist, as you say you're doing. (I used to bend my wrist to hit the backspace key; I got a keyboard with the backspace key in the middle and it made a huge difference.) But my recollection is that you're supposed to do as little moving of the hands as possible. Wikipedia seems to confirm my recollection: http://en.wikipedia.org/wiki/File:FingerHandPosUSA.gif

I was lucky enough to not know VIM when I switched...