This is a great thread, with some great observations as well. It is so interesting that the top four have been so dominant, and that their tactics are so different.
In my opinion, they operate in the Zone more often than the rest of the field, seeing the ball slower and much more in present time. They are also more complete technically, have less weaknesses to exploit. They serve consistently well, both in power and accuracy.
i like Sureshs analysis. Players are going for more winners, more forceful shots, and still, some incredible long rallies between the top players occur over and over. Such is the speed and the brilliance of the top four.