First, it was the whole startup craze; TechCrunch, VentureBeat, GigaOm, etc... Then being exposed to startup job adverts on LinkedIn and other career sites... All these media sources together guided my decisions.
That's not advertising at all - that's news and culture. There's no shadowy conspiracy paying techcrunch et al to talk about how great big cities are. Job adverts, the only advertising part of your post, don't sell a lifestyle generally either - it's just a list of what they want and what they offer.
Tacoma in Washington State puts up billboards in Seattle every so often, targeting techies (e.g. a campaign a few years ago boasted how much better broadband was down there).
I have seen plenty of ads for jobs in North Carolina and other low cost of living locales whose call to action is "move here and pay less rent (plus have a job that might not suck)."