Ok so at 31 he has not declined. Perhaps Aggassi and Sampras never declined either. You can't seriously believe that at 31 you are at the same level as at 24.
I said already he has declined but to a very less degree. And those who are saying that his movement was quite elaborate in 2004-07, also bear in mind that with experience he realized he doesn't need to move that a lot. he has become quite smart as well. So as much as his movement is restricted it is also by choice that he did.
And apart from Nadal and Djokovic, other players are also not playing him in awe as it used to happen like Roddick or Gonzales or Hewitt did, Like Tsonga who takes attack to him. The Tour has moved on.