Nice discussion here folks. Enjoyed reading the posts so far.
In the video referenced above I explain that the WWF is driven by the motion of the arm. Jeff Counts (hi-techtennis.com) compares this motion to lifting and turning over a lever. Roddick and Andreev are good examples of this type of WWF.
But there's another way to hit a WWF. Federer is a prime example. Where the path of the arm doesn't control the low-to-high motion of the racket as much and doesn't cause the WW follow through. Instead, it's pronation that does the trick.
So there are two types of WWFs. Each works just fine. BUT from a recreational player's standpoint, I think the "lever" one is preferable because it's easier to learn, doesn't require amazing timing, and is more stable.
(Ever wonder why Federer goes on "shank sprees" on his forehand? Even the GOAT goes cold occasionally and loses his timing. A good indication of how tough this technique can be.)