i've read a few articles about this over the past few years, it's interesting that a lot of the argument for maxing shit out is due to the ipod and the fact that a vast majority of people don't listen to records anymore but playlists. and no one wants their track to be the weak track in the mix or playlist so labels push for mastering engineers to max it out.
i'm not defending this tho, i have no problem using a volume knob and appreciate dynamics. 
actually metallica's death magnetic record was so over the top hot that fans put together a petition to have them remaster the record properly cause it sounded like shit.
worship the potentiometer.