My 2 cents:
TexMex, you say that you found two common denominators, income and education. You say this as if it's a fact; that your thesis has already been proven and needs no more testing. Isn't this rather simplistic?
The denominator you're looking for is the level of self-reliance of an individual, or more precisely, how much self-reliance is valued. It's easy to observe this by contrasting this site with the liberals at DemocraticUnderground, which we do in the DUmpster section. You see, they believe that the word "bootstraps" is a dirty word. It makes them downright angry. Whereas we here, take pride in whatever accomplishments we've made on our own steam. They get disgusted at people too "proud" to take public assistance; most of us here, if we ever required it in an emergency, quickly got off it ASAP and rarely discuss it.
In rural areas you will see a high level of self-reliance. People proud to live off the land, and incidentally, taking very good care of that land. They are not interested in "social services" as they view that as government meddling, and being a ward/serf of the State. They want no part of this, regardless of income or education.
I have never lived in a big city, packed together. I'm guessing that they have more of a mind-set of relying on a collective body for life-in-general, so they are more receptive to a liberal/left POV.
If you're exploring this in a scholarly/academic way, I would veer away from abortion and gay marriage. This is a false avenue. These are "issues," you are searching for the core of one's being. Which, BTW, makes broad generalizations all that more dangerous.