I believe that 12.6% is the fraction of the national audience that CAN receive one of these stations, not that DO WATCH.
Nevertheless, that's huge. (FCC regulations limit the ownership of stations by a single entity to something less than half the country's potential audience. That's one of the things that keeps somebody with money from buying up a bunch of cheap UHF infomertial-and-old-movies stations and starting a new network.)
And as was mentioned, they get a substantial fraction of their potential in a number of markets. (Not surprising: With the media news operations thoroughly dominated by left-wing political correctness and Fox News solidly in the Neocon faction's camp, there's a substantial audience not served. The same forces that drove viewers to Fox when it started will drive many of them to any outlet that actually covers Liberty Wing / Libertarian issues.)
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"Obama’s Economists: ‘Stimulus’ Has Cost $278,000 per Job."
That means: For each job "created or saved" about five were destroyed.