By the way, I wouldn't read too much into these stats or any of the stats that I have posted, for several reasons:
1) This is a rather small sample set. 281 games isn't really that much to base anything on, especially considering that there are no more than 15 wins per country.
2) There is not really that much to assure quality play. Sure, it's the leagues/tournaments, but the entry criterion is quite varied and still there is some impact from CDs/NMRs
3) The various competition formats biases play. For example, the leagues are affected by meta-gaming; there's no incentive to reduce the size of the draw in the masters; and the GFDT was PPSC while others were WTA.
Also, I am disinclined to believe that there is a "best-country". I think that a particular player might have a *personal* best country(ies), which would be largely dependent on personal style and strategic mindset, but still quite possibly be any of the 7 powers. I do certainly think that there may be a bias in the "personal best country" across this website. Thus, any statistics comparing performance between countries may just be measuring this bias and not necessarily any inherent bias in the game.
While the game is asymmetric, ideal strategic players should compensate for these asymmetries. In practice, the success or failure of a particular country is due to a complex combination of these asymmetries with the strategic mindsets and playing styles of the players involved. Any bias in the performance of a particular country may have more to do with a bias in the personal styles of the community of players. The game does not leave any county as doomed to fail or destined to win.
In short, I don't think these statistics measure the game, but rather the community.