the twisting of the hips really does increase control.
Ignoring all the petty squabbling, this really works for me, point your cock where you want to be going and look at the exit then allong next bit of trail. Doing this automaticaly puts your outside leg down, leans the bike into the gap you've just created under your inside leg, unweights your inside foot, straightens your inside arm and raises your outside elbow.
You could try and do all that seperately, but just moving the hips seems to shift everything else without having to think so much.
And looking at that pic of the DHers Vs Hart, the difference is they're still hovering over their saddles, he's twisted his body and now the saddle is somewhere under his thigh rather than his crotch.
That and lots of practice, after a few rides really struggling riding in a new area (which had more corners and less techy stuff) I took the BMX out the shed and did laps of the garden (which pretty big and has a fair slope to it) kept cornering untill I was drifting both wheels, digging the inside pedal into the ground and dismounting so gracefuly I was barely jogging off the bike when eventualy the laws of physics dictated the cornering not technique. That and riding pump tracks with really tight berms teaches you to look out the exit not over the top.