So, how old are these "must carry" rules? Are they more set up for pre-cable TV era?
I assume these rules have more to do with lobbying/bribes than any practical reasons, like distance.
(And yes, I think of campaign contributions as bribes.)
They've been updated here and there, but are largely of the era when cable was the newfangled thing (the fear was that the cable company would carry only certain broadcasters, leaving others out of the mix).
The markets are defined and can be changed based on the criteria I mentioned earlier from the law, largely distance (Huntington, Charleston, and Columbus are all virtually equidistant from Athens as the crow flies) and broadcast signal propagation (if you look at the maps in the link Alan provided, you'll find that signals from WV propagate to Athens county better than Columbus).
The market altering definitions that could be interesting in this situation are those of shopping and labor patterns and historical ratings. I'd have to guess Athens has stronger ties in shopping and labor to Columbus, and would assume the stations there would've rated decently, given how many people (students, profs, etc.) are transplants or have some connection (even if it is the god forsaken university up there) to Columbus. Or, if you didn't care which market it came from, you may choose Columbus news because the production quality is markedly better (but I probably over-value that aspect).