Loud Commercials Actually Not That Loud, Just Startling
In essence, a typical drama will have moments of loudness and moments of quiet, and commercials that follow the show have to respect the same maximum as the show. However, unlike the program, commercials can simply max out the volume from start to finish, causing a "perceived" or "inconsistent" loudness that's just barely lawful.
As you well know, British regulators are stepping in to make sure no ad is "excessively noisy or strident," but the situation in America could get worse post-2009. You see, digital broadcasts have a wider dynamic range (or loudness spectrum), leaving more room for annoying salespeople to totally invade your eardrum. Nevertheless, the article linked below is a must-read for anyone who has ever been enraged by a "ridiculously loud commercial." [Source: Cleveland.com]
[Image courtesy of Derrick Logan]