Nadal hits mostly buggy whips nowadays.. So he is not a great model.. unless you want to hit like that..
I think its wrong to think about the WW forehand the way Will does. Its not about a way to generate extreme topspin (though it can) its about swinging across your body with a loading of the outside leg while turning over the hand..
With a traditional forehand you are swinging through the ball and finishing up high so its like a low to high thing and with the WW forehand you are swinging more across your body. Thats why the finish ends up lower (along with the hand turning bit).
This guy explains it better then Coach K or WH IMHO..
As for the wrist I think its pretty much just along for the ride - it lays back during the foreword swing because its held loose. I think the WTA players tend to lock it laid back and that takes away technically from their forehands. What you want is low grip pressure.. That's way easier said then done..