Weather is actually a very important factor. In 1996 the courts played very fast (I think partially due to the weather) and the semi-finalists where Sampras, Kafelnikov, Rosset and Stich! It makes a big difference at Wimbledon too.
Oh, I totally agree, but seeing that Nadal won't encounter the ballbashers he typical has issues with, it won't make a huge difference to the eventual outcome this year: Nadal wins.
If, on the other hand, Nadal was to face Gulbis or Soderling early on, it could have made a difference.