The rules for local stations are different for satellite providers than for cable. The FCC has a list of what it calls "Significantly Viewed Locals" for each of the Nielson DMA markets in the nation. These are channels that are outside your actual DMA, but because of geography can easily be received there and are watched by a large number of viewers in your DMA. Cable companies often carry these "Significantly Viewed Stations" on their systems in addition to the assigned affiliates for a DMA.
In my experience I've never seen a cable company carry these outside network channels in HD though, only in SD. Where I'm located in the Greenville-Spartanburg Market some zip codes get some of the Charlotte, NC stations in SD on cable, but not in HD. I guess to protect the assigned network affiliates.
Satellite providers have to go by stricter rules to carry these channels. Dish doesn't offer any of these "significantly viewed channels" but DirecTV does carry some of them in very, very few markets. DirecTV calls them "Neighboring Local Channels" and their availability is usually dependent upon what zip code you are in. I know there is one county near the Georgia/Tennessee line that gets all of the network affiliates from Atlanta and from Chattanooga, TN because of this rule. For a satellite provider to carry these "Neighboring Locals" the channel must be recognized by the FCC as one that is "Significantly Viewed" in that area, and they must compensate the station for these out of market viewers. (usually at 50% of the rate they pay to carry it in market)