And a breakdown of the unaffiliated grouping: (The sample size is said to be 35,000) Atheist: 100k+: 28% 50-100k: 31% 30-50k: 20% <30k: 21%
Agnostic: (whatever the difference in reporting means) 100k+: 25% 50-100k: 35% 30-50k: 22% <30k: 18%
I think in this example, religions affiliation is mostly an indicator of social and economic class, educational trends and the economic reality of immigration opportunities (like in the case of most Hindus) rather than the prevalence of certain religions to earn more. It's also interesting to note that the makers of the graph choose to include such small groups such as Hindu and Buddhist (At .4% and .7% of the population) and attribute the atheist and agnostic population to 1.6% and 2.4%
Further differences in these statistics are the age breakdowns of the different groups and the cultural and social trends that influence the senior members to remain working a longer time. There are differences between religious belief between age groups, and differences in income as well (generally getting higher with age).
The study goes into detail, comparing the educational levels of the different religious groups. Compared to the national average of 11% with post-grad degrees, Jewish and Hindu practitioners are at 35 and a staggering 48%. Atheists and agnostics are a about tied for fourth at 20%, after Buddhists at 26%. Gender seems to play an issue as well, for example atheists are more than twice as likely to be men.