Sigh... I give up on trying to explain this every 2 weeks.
Here's the deal:
Some people intentionally flex their wrists. Some people don't.
Most pros today do not intentionally flex. (we're talking typical rally ball here, not some situational out of position off balance type of shot)
It happens naturally as a result of the stretch-shortening cycle. (ssc). If you don't know what ssc is look it up.
Players who don't use ssc and use their wrists intentionally seem to have a mental block or something when it comes to the possibility that a different type of swing can exist. No matter how many threads there are, how many explanations by top coaches on websites there are, testimonials from people who use this technique etc etc they just can't see it or won't believe it.
I'm telling you that you can swing and get tons of spin, more racquet head spead, a smoother stroke and better follow through using ssc as the main engine and not doing anything with the wrist. The pics posted in this thread are of players who all use this technique. You can use ssc to engage flexation as well as pronation. Trust me. I swing w/ this technique. It takes a LOT of work to get rid intentionally flexing during the swing. You need to get the kinetic chain working correctly from ground to racquet head. Once you learn it you'll see that it's easier, easier on the body and contact feels better. If anything a player who is swinging with this technique will sometimes give a little intentional radial deviation on the wrist.
IMO you need to have a good core rotation to swing this way. Arming the ball seems to work against / prevent / hamper a loose wrist-no intentional flex-ssc swing.
I used to be a wrist snapper so I understand the resistance. And there's nothing wrong with intentionally flexing. It's just another way to swing.
Look at Kohlschreiber's here. Look how loose and fluid the wrist action is. It's as if his very loose wrist is made entirely of rubber. This is the ssc action. http://www.youtube.com/watch?v=K9cR_S7jakA
And fyi, to a poster above... there are no muscles in the wrist.