Speaking about djokovic worrying how to stay #1. That can sure get in the way of playing good tennis. I know when Sampras was going for year 6, he got people to figure out who he had to beat, and who was going to have to lose, and how the ranking worked to end the year number one. It can be very nerve wracking.
I think Andy's got it right ... Win your matches.
I think that's why both Andy and Lendl talk about getting the results and letting the ranking look after itself. That seems the best way to me.
Life on the tour must be stressful enough without getting into all the different calculations for the rankings. I don't see how anyone can focus properly on playing with all that in their head.