You are making it sound as if it's easy, and you are assuming he has the capability of remain and consistent as Federer in grandslams as well as keeping up the high level of play.
Although Djokovic is really smart with scheduling and is physically fitter this year, he is showing signs of burning out during this half, which is really one of the prices you pay for winning. I can see his play is no where the level it was in the first half of the year. Even at Wimbledon there were some signs that it was coming.
I have high respect for Djokovic has achieved, but I have my doubts about how long he'll be able to keep this up.
There is one key reason why Federer managed to consistently dominate the tour as well as delay his decline and remain as a Top 3 player. Federer's game is nowhere near as physically demanding as Nadal or Djokovic's. Nadal was originally and mainly a defensively oriented player, with certain offensive capabilities, in return he went through injury and early signs of physical decline are showing mainly in his speed. Djokovic is still young, and because he is generally more offensive, I feel he'll last longer. However, he is still really defensive in matches, he likes extending the rallies a lot more than actually finishing it off quickly, so we can safely say his game is also physically demanding albeit not as physical as Nadal. When you look at Federer on the other hand, his game is the least demanding. I don't you will find a more efficient game than Federer when he was dominant. He is mostly aggressive, but he did have some exceptional defensive abilities. He generates the largest amount of power with the least amount of effort. He relied more on his actual footwork, positioning, and anticipation rather than pure speed. And when he was on the defensive, he would turn it into an offensive position in a matter of a 2-4 shots, he doesn't really continuously stay on the defensive and let the opponent continue pressuring him and then gradually force the error or dominate the rally. His relaxed style of playing and fluidity only continue to help cut the strains on the body. The reason he's declining however is because his footwork isn't that good anymore, however somehow I doubt it actually physical reasons, since he was fine at the AO 2010 and WTF 2010. Federer's game is more demanding technically, requiring extremely accurate timing and focus as well. It's mainly that department that Federer is declining now.
Djokovic has a large amount of potential, but in order to really achieve and surpass what Federer has he needs to smart about the way he approaches the game, because the unreal defensive abilities don't last forever. He has a solid game, with no particular glaring weakness, good of both wings on the ground, exceptional at the net, reliable serve, excellent returning abilities. He just needs to shift a bit more to the offensive and he should be fine.
