Originally Posted by
Danosaurus 
I work for a major cable network (several actually) in both media prep and master control and I can tell you it is normal to see some shows or commercials in 4x3 (with black pillar box, or side bars) and some fullscreen 16x9. Worst is letterboxed video in 4X3, where you get bars on top, bottom and sides but again that is normal.
Unlike other channels that will arbitrarily stretch 4x3 video to make everything they broadcast fullscreen, we are very meticulous about maintaining the correct aspect ratio for the home viewer. Unfortunately this means it is constantly changing because our media comes from many different sources.
Some of our programs are still upconverted 4x3 SD shows that will have black side bars, though most of the new shows we get are now produced in true HD 16x9.
Same with commercials and promos...they come from many different sources and can be either 4x3 upconverts or 16x9 HD.
The point is that if a channel is broadcasting proper aspect ratios, you will probably see it change all the time, from program to commercial and possibly even within a commercial break. At least until the day when EVERYTHING is produced in 16x9 and the old stuff is purged.
This is all assuming that your local provider is not tweaking anything downstream from us.
Also, the correct setting for your television is 16x9 or Just Scan. I can't stand it when I see displays set to "zoom" or whatever just so that 4x3 content will fill the screen. Looks horrible. You're supposed to see those black bars on the side!
On a related note, since our material does come from lots of different places...various post houses and production companies...the audio/video levels and quality can be all over the place. We try to make them as consistant as possible, but you will still see variation. That's why I think it's never a great idea to evaluate or calibrate a television with broadcast material.