Loudness of TV Commercials

Why do some TV commercials seem significantly louder than the program materials to which they are attached?
The rule, as I remember it, is that a commercial can be no louder than the loudest MOMENT of the sponsored broadcast. This means, if you are watching an NBA basketball game and somebody hits a game winning shot, the commercials that come afterward can be played IN THEIR ENTIRETY at the volume level of the moment when the crowd went wild.

Reason number 13,245 why I don't watch TV...

Maybe to explain what Ghostrider said, the commercials are broadcast not at the volume of regular dialogue level for programming but at the max volume(explosions,etc). I used to set my Fosgate Model 5's dialogue setting at high during regular shows then hit the button again when commercials came on. This attenuated the volume if the remote was within reach. My family got pretty good at it. Dan
TV has always been more enjoyable when the volume was off and the stereo was on...win/win...
"The NTSC TV system uses signals transmitted during the retrace interval at the end of several scan lines to signal TV stations on signal equalization and among other things, commercial cueing. I always wondered why no one built a TV that could read the cues and mute during commercials, or a video recorder that could use this info to skip commercials."

Toshiba made a VCR that did this, I had an RCA version of it, called "Commercial Advance". It actually worked pretty well. After it was done recording, it went back and marked all the commercials. Then during playback it automatically fast-forwarded through them. I would estimate it worked on 90% or better of the commercials.