Sorry...I thought the ATP had the correct numbers.
My argument to J99 is that Nole is more efficient than any other player, by quite a lot. And I think the argument still stands.
So let's count just the events where they played and earned points towards their total.
Federer played 15 events, earning a total of 8920 points. Novak played 13 events, earning a total of 9910 points.
That's an average of 594.6 points per event for Roger and 762.3 points per event for Novak. So Novak earned on average 28.2% more points than Roger per event, and Roger is the #2 in the race. The rest of the players are much less efficient.
Given these numbers, it makes sense for Nole to play fewer tournaments than the rest of the field...He can always change his mind if he loses early in Beijing or Shanghai.