It's really quite simple. A channel is local/regional/national because they buy the rights to show programs in a local, regional or national area!
I'm not being funny here. It's just that simple.
TBS is a cable channel that buys the national cable rights to its stable of programming. TBS also buys the local BROADCAST rights in the Atlanta TV Market for the same programming. Essentially, WTBS channel 17 Atlanta is the sole broadcast affiliate of TBS cable. WTBS Atlanta has about 10 hours of programming a week that is different than TBS Cable for various reasons, mostly dealing with FCC requirements.
Regional sports networks are regional channels because they buy the right to broadcast games within the region of the local teams. The national rights are much more expensive and can be purchased by other networks. Sonce each individual league determines the marketing area of their respective teams, the regional sports networks areas are not confined to specific TV markets. They are rather odd at times.
A local channel can be distributed nationally without being a "superstation" as long as it owns the national rights to the programming they carry. Sky Angel right now distributes no less than 6 broadcast channels from around the country.
WGN 9 Chicago and WGN Superstation share only about 40% of their program schedule. One is a local broadcast channel, the other a national Cable channel.
Where confusion comes in is in the case of the satutory "Supertations" that remain. WWOR, WPIX, WSBK, KWGN and KTLA are the only excetion to the rule. Why? Because they are vestiges of an earlier time in Cable history when it was accepted pratice (though not quite legal and still untested in the courts) for a satellite operator to stick an antenna up near a transmitter and redistribute a popular TV station nationwide. This was usually done for baseball games. WWOR used to have the Mets, WPIX the Yankees, WSBK the Red Sox, KTLA the Dodgers and KWGN... well like I said, Usually. The Rockies came about much later.
There were dozens of "superstations" around the country. But finally the copyright contracts began to be enforced and Congress stepped in to exempt the few stations that remained from the law that would have seen them yanked from cable line-ups.
See ya
Tony