Actually salmoneous is correct. Within a few years, everything will be presented widescreen if they were produced widescreen, but if they were produced with the 4:3 aspect ratio then many (but not all) networks will broadcast them with pillar bars. There are a few networks (TNT, A&E, etc.) who regularly reframe old programs to fill the wide screen, but even then, they don't always do it the same way. Sometimes, they just stretch it horizontally (yuck). Other times, they do a better job and zoom in, but then you could have some things cut-off at the top and bottom.
Incidentally, a lot of folks on the high-end video forums I visit HATE the practice of filling the screen. So there is continually a fight between those folks and folks like DLBDS who want to see their widescreen televisions entirely filled. I don't actually think either side will eventually "win" but rather there always will be some places that go one way and some places that go the other way. (Of course, as time goes on, 4:3 aspect ratio source material will become less and less of an issue.)