With wealth distribution being a hot topic in the real world, one demographer/World of Warcraft enthusiast tried to derive what the income inequality is within Azeroth. The results of his survey of nearly 2500 players -- with an admittedly great margin of error -- is that the wealthiest one per cent in the game control 24.25 per cent of its gold.
In America, the figure is something like the wealthiest one per cent have 40 per cent of the wealth. However, the lower 75 per cent of World of Warcraft players control just 14 per cent 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 (October 9 to November 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.