I was going to make a shitty response because this community sometimes acts retarded when having something explained to it, but I will help out because specs is so nice sometimes. The reason why shit does not make it on TV is because of a couple of things: 1) the FCC, 2) social dialects.
The FCC was created to regulated the airwaves back when radio was huge. Because radio was so big, and because people did not have as much freedom from stations, this continued to the first stations on TV, the FCC would regulate the language to keep it non-offensive to everybody. Now that we do have cable and there are literally hundreds of choices, there is not much reason for them to exists. If you compare the subscriptions channels with the broadcast ones (showtimes, cinemax and HBO vs ABC, NBC and CBS), you will find that the subscription channels are able to do whatever they want on the airwaves. This is because not everybody has access to them; and because of their exclusivity (you need to pay to access it) they are not subject to regular airwave rule.
Social dialects are a bigger issue because a lot of funny things happen in our culture and they have all sorts of wacky interactions. The important part to understand all this is that status has a lot to deal with how language is spoken or written. Our rules for grammar are not descriptive (they do not explain what is going on) they are prescriptive (somebody arbitrarily decided we were to speak and write a certain way, usually somebody with influence designated this). Now that we have that out of the way, we also have to deal with the fact that we do have regional dialects. This alter the way a sentence is formed, how certain sounds are pronounced (an accent comes from the difference in pronouncing these sounds, coming from a different language is a little bit different than when dealing with dialects) and more importantly it also varies the lexicon. These all happen from region to region, but they can also happen from different society section (poor people to rich). We know this happens because of experiments done in New York and London on the various ways certain groups of people speak. In both countries you could easily designate how a certain group would pronounce certain sounds. This does not mean that some feature like dropping the “R” out of certain words were not present in certain classes, although in some places they were absent, simply that it was less likely for a certain group to do this.
Words that are considered taboo are completly cultural (in Yanomamo society it is forbidden to speak the name of somebody who died aloud, but they will still call you a cuntface). Combined with the stuff from above you suddenly get the influence of upper crust people, these are usually the most likely to get a lot of govt jobs, in the case of the FCC we have Colin Powell’s son who was raised in a Republican household, which means he learned certain things by being the son of a military person and all sorts of other great stuff present in his background, combined with the history of the FCC and its obtuse policies, we can’t say shit on TV. So if we could go get Mr. Shatner some linguistic and anthropology classes we would be set. This is also mostly why, Mr. SoVI3T, you cannot fuck anybody on broadcast TV but watch a whole lot of bullshit on showtime.