actually if you took a closer look i will tell you exactly what federer did to blake.
He took away James's forehand by hitting it to his forehand. Most people dont notice this but James likes it when his oponent hits it to his backhand....this way he can run around the backhand and hit his inside out forehand. What federer was doing was instead of just keeping it to James's backhand...he hit it down the middle to James's Forehand side. What this did was it took away James's biggest shot and forced him to try to hit a winner crosscourt with his forehand which is not likely his best shot. Anyone who plays knows in order to create angle one must be given an angle by hitting down the middle all James could do was hit a deep shot and come to the net..his volleys failed him and this took away from James's game
Federer did something I have never seen before and that is taking away James's forehand by actually hitting it to his forehand.