I don't think it's purely regional. I went to a talk about high-school CS education a few days ago by some NSF guy, and the statistics he was quoting were that only about 2-3% of U.S. high schools offer AP CS classes. So they're going to be rare anywhere in the country.

Looking at the College Board's numbers for test takers, there are about 19,000 who take the AP CS exam per year, less than one-tenth the number of students who take the calculus exam.