This topic has been discussed ever since talk radio advertising began in 1922 with an estate agent. In those days the ads were deliberately made louder since the company paying for the advert wanted be sure that the listeners heard it.
For many years since 1957, the BBC and radio stations quite blatantly denied that the volume of advertising was louder and proved it by showing the VU (volume unit) meter did not go excessively into the overload region during the time the advertising was being played.
Recently, Multichoice was taken to task for doing the same thing. They achieve the higher perceived volume by lowering the range between the softer passages and louder passages of the advert.
When it is money talking, the broadcaster must take heed as they get paid for what they deliver. If product A's advert is more effective then product B, given everything else the same, then consumers might be tempted to try product A instead.
There are devices under development which will automatically mute the advertised sound, but strangely, it is encountering some resistance...
