"Liberal Protestants" are not so liberal after all, at least economically speaking.
The Atheist/Unitarian/Agnostic dynamic is quite interesting with regards to economic issues, as well. My theory is that agnostics are more conservative fiscally because they don't really have an agenda(and tend to have other traits corresponding with fiscal conservatism), whereas atheists tend to be fairly staunch secular humanists, given the potential stigma of the label.
I was a bit surprised by where the Quakers ended up. Granted, it may be due to small sample size, both in the poll and in my personal experience, but the local Quaker congregation is definitely left-of-center economically rather than slightly right-of-center.