I'm a production director of a radio station so I'm constantly working on commercials. Although I don't go so far as to brickwall things, I do use a variety of compressions, limiters, and EQ to balance out the sound of a commercial -- usually to even out a vocal performance or to make it work with music and sound effects better. There's a cookie cutter and hamfisted way to do it and then there is actually using your ears to do it correctly. That said, what was done with the 5.1 remasters of the Genesis catalog were a travesty. Any dynamism was lost because suddenly what was supposed to be a quieter acoustic section was as loud as the full band playing all out. That's not the way it's supposed to sound.