^ I believe that you are coming away from this with an erroneous notion of what is going on with these serves. Murray, Federer, Vaidisova, Sharpova and many other servers are still looking at the ball very close to contact. They are obviously watching the ball at the trophy phase and are still watching as the tossing arm drops and as the racket head drops. Even at the "big L" (when the racket arm becomes fully extended), most of these servers still have their eyes trained on the ball -- even tho' the head has started to move/turn.
Even Roddick appears to be looking at the ball at the "big L". However, his head quickly turns and looks forward from this point. Not so for the other servers mentioned above. Note that the time it takes to move the racket head from the "big L" up to the contact point is very short -- it would be measured in milliseconds or centiseconds. For this reason alone, I maintain that most servers are fixated on the ball very close to contact.
Furthermore... even when the head moves/turns, the eyes can still adjust their position so that the foveal (central) vision is still trained on the ball. It is not that difficult for the eyes to point in a direction that is 45 degrees offset from the primary direction of the head. So... even when they are not directly facing the ball, the eyes can still be looking at the ball.
Bottom line: It is probably best for most of us to watch the ball as close to the contact as possible. I've seen plenty of players who pull the head down much too early -- before the "big L" -- or even before the racket starts it's upward swing. If you decide that it is not important to watch the ball to contact, you may end up pulling your head/eyes down much too early as a result.