You guys can see in Djo's photos that toly posts that the wrist angle between photo4 and the last photo changes significantly, as suresh points out.
It cannot be the effect of pronation.To me pronation would be like turning a car's steering wheel. You can do that without changing the wrist angle. Clearly these top guys manipulate their wrist joints. Their wrist angle wrt the forearm segment don't stay fixed through the stroke.