Idiotic question.
How-many grandslams would Murray and Roddick have won if not for Federer @ his peak? Being a Grandslam champion has nothing to do with luck and playing player's @ the peak of their game. Winning a grandslam, regardless of opposition is a hard feet and not one you can get an easy ride in. Current breed of player's and era's shouldn't be made such an aspect of.
Plus, I don't believe Nadal is in the best form he's ever been in on Clay.
At his best no one would be Nadal on clay, not even Borg.
At his best no one would be Federer on grass, possibly Sampras.
Hardcourt is a toss up, although currently you would say Djokovic, Murray or Federer on top form would push him very close.
Just remember, form is temporary, class is permanent, lets see how long this current streak of good form from Djokovic can last for before we start talking about Djokovic in such classy terms. (And that mainly applies to his CLAY season)