That has been my experience, too - guys from more rural areas, especially farming areas, wear briefs more commonly.
I might have told this story here already so forgive the possible repeat. I know a guy who went to the U of Tennessee and he wore boxer briefs at home. He also was really into hunting and fishing, which was a bit unusual for our area (and he now actually works a farm). When he got to U Tenn he quickly started associating with other rural boys who liked to hunt and fish and he went on a weekend fishing trip with the guys. He told me that he was the only one in the group NOT wearing tighty whities which made him feel so out of place. He quickly went out and bought a few packages of briefs and started wearing them regularly, and definitely when hanging out with the boys on hunting and fishing trips. Several years out of college now he still wears tighty whities as his standard underwear.