Why does height matter? I mean if it was power it would be different. Power is an attribute that is necessary in tennis. But height isn't the same as power and isn't necessarily even correlated. Size would be more important. I mean I am pretty sure that Serena can squat or bench more than Sharapova and I think we can say the same about Ferrer and Djokovic. I guess it does make sense in terms of serving, but considering that Federer is the only one in the top game with a great serve, it isn't all that vital.