Sorry for another waffling post.
I wish more people would waffle like that because it all makes perfect sense to me! Thanks ATL. Also Andy has said that after matches he needs 9 hours' sleep to enable him to recover fully for the next one, so if he's being deprived of that on a regular basis it's no wonder he was so tired.
As for Djokovic, there's little doubt that his priority is tennis and winning as many titles as he can. Federer seems to have got the balance right, but then he travels with an army of nannies, etc, to look after his family, which means that at least he can be with them when he's off-court without having to exert himself.