From The Economist:
Have Ms Williams and Mr Federer discovered a new method for older players to compete effectively? Both of them have unique skills that are unusually resistant to the ravages of ageing. Ms Williams’ greatest strength is her remarkably fast and accurate serve, which is easily the best in the history of women’s tennis. She hit 24 aces in her semi-final win against Victoria Azarenka, tying the single-match record on the women’s tour, and set a new record for total aces in a tournament with 102. Opponents can only take advantage of Ms Williams’ declining foot speed if they manage to return her serve. Moreover, the high number of points Ms Williams wins with a single shot prevents her from tiring too quickly.
Mr Federer’s corresponding advantage is his versatility. Whereas Mr Nadal often tries to wear down his rivals with his punishing strength and stamina, Mr Federer aims to disrupt the rhythm of fitter opponents by mixing up his shots. He has become better than ever at keeping his adversary guessing, even though he is much more likely to lose energy and focus over the course of a long match than he once was.
Yet it was no coincidence that Ms Williams and Mr Federer both ended their title droughts at the same tournament. Wimbledon is the only Grand Slam that is played on grass, where tennis balls bounce lower and retain more of their speed than they do on other surfaces. That leads to shorter rallies, reducing the physical demands on players, and favours the aggressive, risk-taking style of tennis that both Ms Williams and Mr Federer play.