Of course, that isn't always true. NOVA and the Denver suburbs are clear counterexamples where rapid urban expansion is liberal rather than conservative. I have a feeling that it has to do more with how wealthy the newly built areas are. Nearly all new development in California is built by the very wealthy while the middle and lower classes slowly spread outward from the cities into areas vacated by the rich. This is not the case everywhere else, which may be due to higher concentrations of wealth in California than elsewhere. I'm sort of guessing here, but the cases of NOVA and Denver certainly don't corroborate the theory of conservative new developments.
Denver is a bit different from NOVA. NOVA even the exurban areas are moving very quickly to the left (Loudon, Prince William). The Denver exurban areas such as Douglas and Weld remain very Republican. With that being said unlike many exurban areas they haven't become more Republican as they have grown, if you look at the margins (compared to national) they have become a little more Democratic, though the amount vote total margins have helped the GOP. However, what is happening in Denver is those older suburbs Jefferson &, Araphaoe for example are STRONGLY moving Democratic. Boulder which has always been liberal has gotten MUCH more liberal than it even use to be.
