Well, I don't think that Nadal has got quite the aura Fed had during his prime, which we can reasonably consider as over. That doesn't mean he won't win any important tournaments anymore, but less than in the past. Feds domination of the circuit was brutal. In any match, except the FO final against Nadal he was the favourite and he won almost any match too.
Nadal seems more vulnerable on certain occasions, certainly with the crowded schedules of ATP lately. He even lost in Rome, which should have been his in normal circumstances. But Nadal's aura is that you can never say you've won the match against him until the last point is over. Ask Fed, up in the Monte Carlo and Hamburg final, ask Djoko, blowing a lead twice in the Queens final, and also in Hamburg.
I'd say we are talking about two different auras: Federer's is one of elegance, perfection, utter concentration when everything is on. That of an attacking all courter, who, thanks to the nature of his game, will have easier matches and therefore can dominate for longer periods without getting tired.
Nadal's is one of a gritty, never say die player, who can always come back, can always run down an approach and hit a stunning passing, but whose game looks less elegant and needs longer rallies to finish points. Therefore he is a very tough opponent but he wears himself also down due to his style of play. Blisters, tendonitis and other injuries will always plague him and he will have a harder time dominating in an easy way, which doesn't tire him and puts stress on his body.
