Just studying the very best at every sport, I came up with this conclusion years ago.
The ones that are at the very top have one aspect that separates them from the rest. It's not a particular skill, or even work ethic in this case.
It's the fact that no matter how **** poor they are playing, they just find that inner beast and pull it out. Most any player in any game or sport can have a bad day, lose, and chalk it up to a bad day and work on their weakness.
Nadal and Ferrer, along with the other 3? It can be 5-0 40-0 they are down and they just gain another gear. Ferrer played like out and out trash in the first set and most of the second, and he comes alive out of nowhere.
That, simply, is why they are all at the top.