That was my first thought as well, not a very representative sampling of the overall population. Probably not even representative of e-book readers.

Aside from that there are so many factors that could be at play. Distance to bookstores. Same for ease of access to public libraries. Internet and technology use levels. Looking at state statistics probably does not say that much either. The difference between Madison, Wisconsin and Park Falls, Wisconsin are probably greater than the difference between Madison and San Francisco.