I think this question is much different in canada then the US. canadian stats show that if you make 20K your more likely to vote conservative then if you make 10K, and if you make 30K, more then 20K. 40 over 30. 50 over 40. 60 > 50. 70 > 60. 80 > 70. 90 > 80. 100 > 90. 110 > 100. 120 > 110. 130 > 120. 140 > 130... by now, at 140K, the percent of Conservative voters tends to double... but the weird thing is, and I think this is a uniquly canadian thing, is people who make more then 150K a year vote 70% Liberal. dunno why, and neither do the pollsters, but it's constant.
There actually may be some non-monotonicity in voting wrt to income in the US as well. There are not enough multimillionaires to show reliably in the polls, but there is anecdotal evidence that at the very top of the income distribution there are as many Dems as Reps, or more. The polls (especially state-level) would be quite unrealiable as far as high income brackets are concerned (hard to sample enough of these guys, so the numbers are low and errors are enormous). Still, even at the slightly lower income brackets there might be wiggles: people with graduate degrees are not poor, and mostly vote Democratic. True, it seems most in the 100,000+ range vote Rep, but I am not really convinced that once weighted by income that is still true - and it is definitely not true in every state.
This could be the case due to the fact that, above a certain threshhold, you have so much money that you honestly don't care about economic issues all that much, given that you'll probably still have more money than you can possibly spend. I know that I certainly would be in that boat if I had, say, a seven-figure income.
