And seriously, that shows how much he (Federer) cares about tennis and about winning.
Because why other great players didn't do that?
OK, Sampras had Thalassemia, low stamina, he couldn't physically grind out matches, so his only option was winning making winners all night long.
Becker?, OK, he was a very big and a bit heavy guy. Even though he was terrificly strong, he possibly could never win running like crazy from corner to corner for hours. He had a heavy and big body.
But Agassi?, he had great stamina, he wasn't big (5 f. 10 i.). Agassi could have done it....had he been faster. But Agassi was not a great runner, simply. It is possible that he had better results being the aggresor all the time than grinding out matches (even when being the aggresor was failing him).
Federer had the great physical gift that he indeed could do it, and could do it like the best ones.
Perhaps Sampras could have been like that had he had better stamina, because he was quick like hell and cat-like, but he always chose not to (and probably was right, because with his condition his only option was winning dictating all the points).
Federer had the whole package, could do everything, that made him an incredibly difficult player to beat.
I remember Edberg as well. Even though his game was pure serve-and-volley, Edberg was very very fast and smooth when running on the baseline, and a great defender as well when needed, but he had not the great forehand of Federer, so he could not defend that well from the forehand side (he was great hitting backhand passing-shots though, and he hit great lobs too).