I looked at those threads and am confused.
Could you briefly summarize the point you are making by referring me to those threads?
What I see is that hand accelerating hard out of the drop in an arcing fashion. I think what Wegner is referring as sudden acceleration prior to impact is the racket lag catching up with the hand as the arm straightens and the hand arcs across. Basically, the racket head is going to lag my hand as it accelerates out toward the ball in an arcing fashion.
Here's a video. http://www.youtube.com/watch?v=k_6hC2qKnKw&NR=1