Quickly, and without reading, I would say that a potential bias with this survey is that people already have preconceived notions about what "urban" and "suburban" are. I think it would be very difficult to actually measure someone's density preference in a very short survey. Also, what is urban density? What is suburban density? I doubt people know or can visualize the census's definition of urbanized area.
Consider that now a majority of people in the US live in "suburbia", depending on how you define it. Is it surprising that young families prefer the perceived safety of the suburbs in which most of them were raised? They have young children, for crying out loud!
While I'm not trying to completely cast doubt on the message, shady statistics bothers me. I think most of the "planner-types" (at least on here) realize that the high-density lifestyle isn't for everyone. That being said, the market for that kind of living should be satisfied.