It is interesting to see the results if you apply Wimbledon rules to clay, but to do the exact same sums doesn't make sense. Wimbledon does it's adjustment because the grass season is so short. The clay season is much longer, so is already much better represented in the actual rankings. If you are a clay court specialist, you can already pick up extra points by taking part in the many extra clay tournaments that most top players don't normally bother with. If there was a grass equivalent to the South American swing, grass court specialists would be able to pick up extra easy points and the look of the top 20 would be very different.
That's a good point Sparkle - with all the clay tournaments available to play, there's definitely no need for a clay formula. Lower down the rankings it would probably make some quite major changes between the true clay specialists and those who don't have good results on clay at all. It's quite impressive that Andy still comes in at number 5 though - his 2011 clay season must have made a difference there.
I see John McEnroe has joined the debate, saying that he thinks Nadal should be seeded number 1 - I'm sure Djokovic would be very happy about that!http://tennis.si.com/2013/04/24/rafael-nadal-french-open-seed-john-mcenroe