What's to figure out? Roddick has found the leverage actions of the arm, shoulder, body, etc. and a certain timing (very fast) that works for his mind. Federer can't serve like Roddick and vice versa but they all follow the same principles.If we could all figure out how Roddick does it, these threads would all go away.
In another thread, I noted how Roddick's arm is actively pulled downward much further than any other pro. If you use his elbow as a reference point, he pulls his elbow down rapidly more than 18 inches lower from the trophy position (compared with only 3-4 inches for almost all other pros, who usually just rely on gravity rather than active pull-down), allowing him to using his shoulder joint and other tendons/muscles of his kinetic chain as a spring to uncoil more energy upward into the racquet.In a normal serve like Sampras' it's racquet drop then hit the ball.
But for Roddick he's (famous) trophy position is much lower and earlier. His motion just after that position is so much quicker as well than the usual racquet drop of a normal serve.