The FCC Reg on cable coverage is that the television station must provide a signal of sufficient quality to the cable head-end. That can be met by broadcast reception or other means (fiber, microwave, etc.). If a station's signal does not meet that requirement, the television station is out-of-luck. Even if they spend the money to get their signal to the cable head-end, the cable company can drag their feet on carriage.
Once that requirement is met, the TV and Cable must negotiate - MUST CARRY or RE-TRANSMISSION. MUST CARRY says that the cable must carry the station - but not where they carry the channel. RE-TRANSMISSION Is where the parties negotiate for channel position, payments (to or from), and other things.
Local channels without local content are going to lose in the next few years as the cable companies get more power in their negotiations when DTV makes it nearly impractical for consumers to watch local TV for free. Let's face it, people don't put antennas on their houses anymore. No outside antenna - no HDTV!
Dish and DirecTV use the same head-end measurement for their channels. It's a WASTE of bandwidth as there are over 1000 Dish and DirecTV channels showing effectively the same programming - the viewer is ocked out of receiving 200 copies of ABC, CBS, NBC, FOX and others - but the channels are still in use.