In America, the figure is something like the richest 1 percent have 40 percent of the wealth, which would seem to be a greater disparity. However, the lower 75 percent of World of Warcraft players control just 14 percent of the game's gold. That leads the survey taker to conclude that:
The whole ingame economic system is an extremely top-heavy one, leaving large sums of gold sitting idle in the top players pockets kept isolated from contributing to the economy, which is especially detrimental if one considers that a server economy is the simple flow of gold and materials. One can argue however that by holding such large sums of gold such players can more easily influence and correct markets, keep inflation in check by keeping the sums of gold out of the hands of the masses, and provide buyers for big ticket items such as TCG Mounts.
The survey was conducted over a month (Oct. 9 to Nov. 5) and, despite the obvious caveats ("trolls" being one hazard accounting for a large margin of error), it appears the guy who conducted the examination knows how to do so scientifically. There is a great deal more detail at the link.
Report: World of Warcraft Wealth Survey [The Golden Crusade via WoW Insider.]