Sampras "one toss" a myth
Recently Paul Annacone stated that Sampras did not have the same toss for every serve, thus eliminating the myth that he could hit any serve with the same toss. However, he did state that Sampras could hit many different serves with only a very slight variation on his toss, mainly because he could make slight changes in his body movements (i.e. foot position, bend of knees, trunk rotation, and racquet head speed) which would add into a significant change in direction, rotation, and speed on his serves.
Makes sense his serve was so deceptive since we are all taught to keep our eyes on the ball... interesting if any pros watched for Sampras' body changes to try to read his serve, but I imagine that would be unbelievably dificult to do while you're also trying to track the ball.