This has been brought up on the forum a few times before that I know of - my take on it remains that the problem is with the source material itself and nothing to do with your AVR, or system in general. Sometimes it is used directly as a marketing tool, in order to grab someone's attention, the producers of the "spot" (commercial to anyone else not in the biz), will intentionally mix the levels high; you see this in particular with commercials that are targeted for the elderly - presuming that their hearing is not so good anymore, the company wants them to be able to hear what they're selling.
I agree with j garcia - any attenuation or "Night" mode will reduce the problem, but also introduce compression which will lessen sound quality overall. I just keep my finger near the volume button on the remote when I know commercials are coming up.