Well he doesnt have to work so hard on serve. Nads almost went 13 hours in 3 matches from R3 to QF, thats too much.Djokovic doesn't play with less effort, IMO, and being one year younger is not much of a consolation, when he needs 4 (maybe three after tomorrow) just to catch Nadal.
That is one whole season similar to 2011, which is one hell of a task.
IMO, he will do extremely well to even catch or surpass Nadal.