One thing people outside the US may not realize about studies like this is that a very large percentage of socioeconomic breakdowns in the US are proxies for the traditional north-south civil war divide. Compare a map of income inequality by state and overlay the 1860 election and you'll be looking at extremely similar maps.

So, to a large degree, this study is merely saying that upper income people in the US South are less generous than upper income people elsewhere in the country, something that isn't a surprise to anybody to anybody who even remotely follows US political trends.

http://visualizingeconomics.com/blog/2007/07/17/united-state... of income inequality by state