That is what I thought you meant, but I wanted to be sure. It is a common misconception, but humid air is actually LESS dense than dry air, though it feels like the conditions are "heavy." Thus, if anything, balls travel faster through humid air (marginally, not noticeable) rather than slower. And the temperature makes little difference in the speed of the ball.
It is obvious that you are just looking for things to comment on RG being faster and why Nadal lost. Certainly, you can't think RG is faster than Wimbledon last year can you? Yet, Nadal won that with no troubles until Fed. How come he had such troubles this year at RG, when it is undoubtedly still slower than Wimbledon last year, which he won? He lost, he had a bad day, Soderling played good. It was not the courts, the balls, his strings, his pink shirt, or anything else. Stop finding excuses, it is getting old.