I have to disagree with your characterization of people in suburbs. The only anecdote of trusting behavior given in the article was of a rural farmer in an isolated area - and it was given in contrast to people from urban New York or New Jersey coming up and being amazed about it.
Here's another hypothesis - tribal or rural cultures will be more trusting by nature. Human beings are naturally paranoid but NOT of each other. If you are competing with other species and the environment for survival, it doesn't make sense to view your own species as a threat. Indeed, it benefits your family or tribe if you all cooperate. However, in densely populated urban environments, your competition is all human beings. If you are metaphorically eaten or taken advantage of, it will be by another human. It's much less likely in a city that you will die because of exposure, or weather or a wild animal. Thus, because the threat is from people, you must be more wary of people.
I'm not super confident about this of course - it's probably both simplistic and wrong on a few levels, but I think whatever the answer is, it's not just that urban people are trusting and rural people are paranoid.
I may have overcharacterized, but I was specifically referring to those in cul-de-sac neighborhoods, not all suburbanites in general.
More traditional gridded suburbs, especially those with large communal parks, probably bely the behavior I described, but I'm mostly speaking intuitively on the matter, as I'm not aware of any studies.
There is existing data that strongly suggests corroboration here. Isolationist and/or segregated communities breed distrust of those outside the community. Cul de sacs are but a softer implementation of that segregation. Buying trends indicate that in most cases, cul de sac purchases are done with less diversity in mind -- whites buy in predominately white cul de sacs, minorities do the same; which just compounds the self-reinforcing price strata already existing within neighborhood communities.
That said, despite your low-brow dismissal, I'm not suggesting that cul de sacs are evil. They are very good at building close-knit, but very small communities. Kids that play in cul de sacs generally do so in plain view of everybody else, and with less traffic interruption, encouraging play and discouraging deviant behavior.
Cul de sac kids have a greater sense of trust with those within the immediate community, but at the expense of less trust for those outside that community -- just as isolated communities tend to do.
It is not a low brow dismissal, appealing to a HN meme doesn't save your position. :) A cul-de-sac is hardly an isolationist community. If anything you could probably go find data these people are more naive or trusting than the norm. Your position is just a rehash of the unquestioned assumptions of "suburbanites" that I think probably have a little but more to do, ironically, with "media conditioning" than even you might think.
My position doesn't apply to all, or even most suburbanites, nor is it entirely critical. I don't know why you're taking offense to it, especially offense that you haven't bothered to refute.
Cul de sacs are insular, and that's considered a selling point of them. I'll grant that they're not quite as extreme as gated communities, but that they exist for the purposes of insulating one from traffic otherwise associated with more frequented byways. That isn't a contrivance, it's their stated purpose. It shouldn't come as a shock that insulation from use as a thoroughfare would extend to insulation from outside contact, as that's the obvious result.
Here's another hypothesis - tribal or rural cultures will be more trusting by nature. Human beings are naturally paranoid but NOT of each other. If you are competing with other species and the environment for survival, it doesn't make sense to view your own species as a threat. Indeed, it benefits your family or tribe if you all cooperate. However, in densely populated urban environments, your competition is all human beings. If you are metaphorically eaten or taken advantage of, it will be by another human. It's much less likely in a city that you will die because of exposure, or weather or a wild animal. Thus, because the threat is from people, you must be more wary of people.
I'm not super confident about this of course - it's probably both simplistic and wrong on a few levels, but I think whatever the answer is, it's not just that urban people are trusting and rural people are paranoid.