I can generate a lot of spin on my shots and while it looks like my wrist is doing it, it is really my forearm. I know this because my right forearm has gotten a litle bigger than my left from playing so much. I also know this because i had wrist tendinitis that was pretty bad, and i simply can not go out there and wrist shots.
Also djokovic does not hit flat, he uses a full western grip and generates a lot of spin. You dont have to roll over the ball to hit with a lot of spin. in fact that can end up being counter productive.