Why did the Republicans only carry 2 of the 10 richest counties in the USA in 2008?

Because many rich people vote on cultural issues just like everyone else, and Rich people are cultural liberals except in the south. Your religion and how often you attend church is a much better predictor of how you will vote than your income and as been for at least a decade. The worst effect of the realignment of the parties under Reagan is that we now have two parties that look after the welfare of the rich, and no party of the working class.