One thing that people might also consider is that the courts across the venue do not play at the same speed. The reason for this generally is the main courts are re-laid each year and so are slower than the others which aren't (Plexicushion speeds up as it ages because it gets smoother - and it happens more than you might think), plus some are exposed to the elements 100% of the time compared to maybe only 80% of the time for the covered courts.
Similarly, the tournament director has said outright that they haven't sped the courts up this year. But, the players have said that Rod Laver plays slightly slower than Margaret Court - yet both would have been relaid. This suggest perhaps that the laying of these courts does have variables which, despite their efforts, they can't completely get rid of.
A previous club I played at had three Plexicushion courts which, when they were about 3 months old, one got a long split about 1m inside the baseline. They repaired that spot and for months it was noticeable grippier despite being laid using the exact same batch of surface material - and that was after only a couple of months difference in use and exposure to the elements. When the courts were a couple of years old they ceased to be the slow courts they once were - they had sped up a lot.
My bet is the balls are 90% of the difference the players are noticing on a given court. They've said the balls are different this year and, to my eye, the conditions seemed a quicker than other years, but they're definitely not as fast as the Nadal's seem to imply.
