The idea that there is a correlation between religiosity and the material wealth of the population is not a new one. To view this as simply measuring relative prosperity against religious belief would be too simplistic.
Many cultural factors will influence this, factors shared in common with many of the countries that have the greatest GDP. Factors such as female emancipation,equality laws, reproductive rights, increased leisure time, greater disposable income, advanced education systems,the dominant political framework and obviously statute and the law.
And when you look at that relationship, it is true that the US is an outlier, a counfounder in that observed relationship, and worthy therefore of examination and discussion.
Another graph demonstrating the linkage between Religiosity and GDP can be found at this link, which is quite interesting.
http://wehrintheworld.blogspot.co.uk/2010/09/chart-of-month-religiosity-and-gdp.html
http://whyevolutionistrue.wordpress.com/2010/09/04/a-correlation-between-poverty-and-religiosity/
From that second link, an interesting observation;
"Why is the U.S. an outlier? Also unclear. Greg Paul, of course, has suggested a modification of the theory mentioned above: religiosity is higher not just when average income is low, but when average life security is low. If you plot religiosity against what Paul calls the “successful societies scale,” which takes into account dysfunctionalities like corruption, suicide, marital stability, and so forth, the U.S. is no longer an outlier. We’re a rich society, but Paul’s metric shows that we’re not such a successful one."
And the % of the population that consider religion to be important to their daily lives;
Germany 40%, France 30%,Canada 42%,UK 27%,Japan 24% Denmark and Sweden around 20%
And then you have Italy at 70% and the US at 65%. Significant outliers.