Nadal is a grinder. He runs everything down on the court. If he doesn't change his style he will wear himself out sooner rather than later. This is part of the reason he doesn't have a lot left in the tank when the end of the year rolls around. I think he makes the push on clay because he can earn a lot of points during the clay season and still stay the no. 2 player.
You could see Nadal's defeat on clay coming the last couple of tournaments. He was being pushed around by Hewitt and Davydenko. Two players who should have defeated him they were playing so well and then choked. He didn't get the choke factor from Fed this time.
Hewitt and Davydenko didn´t choke. Nadal played better in most of the big points as usual.