Federer is actually one of the hardest working players out there. It shows in 5 set matches when he's not huffing and puffing. Not chasing down every ball is part of this style, which only adds to his physical fitness. I remember some commentators saying that he invited a couple of up and coming junior players to train with him in Dubai (Ricardas Berankis was one). They said that Federer's fitness was so good that his training partners had to rotate with each other to rest. When he's warming up on courts where everyone can see him, he is very carefree and almost lazy. But when he's practicing away from the crowds, you can really see he's trying.
And, Nadal is actually a great volleyer. His form isn't the most natural looking and he doesn't come up to net much because that isn't his style. But if you've every seen him play doubles, he's pretty solid