I understand that many disagree with Nadal on this, and I'm OK with it. However, I do reckon there is a point to be made that the tournament featuring the eight best players of the season exclusively should rotate the surface, because of its own nature, which is different from that of the rest of the tournies, slams included. You can't seriously sell it as the truly World Tour Finals if it's just another indoor HC event that just happens to feature the eight best players on tour.
Now if you rotate the surface and conditions you'll be truly representing the tour variety as well as showing the world how the eight best players in the world fare while facing each other in different conditions, not in the same ones year after year. It would actually boost the event prestige a lot. The way it is it's just a "special" indoor HC event, but in no way a faithful representation of how the best players in the world fare against each other... Again, unless we want to call it the Indoor Hard Court Season finals. Then I'm okay with it.