As Patio said most TVs (He said good but I can't bring myself to call my Vizio "good"- Acceptable, maybe...) have something like Volume Normalization. I don't know about commercials (As I don't use netflix or Cable or anything that would have them on the TV) but with some TV Series Blu Rays I found there was some questionable leveling (quiet dialog, loud intros/music segue's, etc), stumbled upon the setting and that sorted it out for me.
PC's themselves will usually have some form of volume normalization or AVLS type feature in the audio properties.