I found it interesting that the sum actually isn't relatively constant. The sum is steadily declining from 1.89M in februari 2009 to 1.65M in februari 2010. Given the ongoing growth of the internet (and the population), the total traffic should have increased, making the shrinkage all the more interesting. I'm guessing there are either Asian sites eating away a substantial market share or that the measurement methodology of Compete has been changing.