I'd understand it if most of the local businesses that forgo an online presence were all 1-4 person, family operations where they're all too old to have a "Google it first" mindset. However the majority of businesses that refuse to register themselves with Google have no excuse. I can search for the closest laundromat, tire shop, florist, etc directly by name and address and the only results will be those sites that scrape the secretary of state's corporate filings.
Google has made the process of creating an online presence the simplest, most painless process imaginable. Google's My Business service gets you on Maps with all the important info (location, hours, services, etc) for free, yet so few businesses take the importance of being a top, location based result. If a business doesn't come up in my location based search it's as good as if it never existed.