It'd be hard to defend NBC's shoddy coverage of these Olympics, considering they broadcast on as many as 5 channels.

But you may have a point, there may be too many sports that just don't have an audience, particularly with the US audience which is NBC's primary concern. When they cut out part of the opening ceremony to air more Phelps interviews, they defended their action by saying they were catering to the US market. I imagine if the US had more dominant athletes in sports like TKD and fencing, then the sport would get more coverage by the broadcast network.

Another issue is that some sports are just part of the Olympics, whether fans care about them or not. I don't know about fencing/epee/saber, but who really cares about sports like the shotput and hammer throw? Probably not many people, but those sports have been a part of the Greek sports since ancient times, so they will probably always be a part of the modern Olympics. FYI, fencing and shotput have been in the Olympics since 1896 and hammerthrow since 1900.