The main ones being the movie studios, which couldn't care less about ad dollars, they only care about selling movies and this WON'T sell movies.
The movie studios are complaining constantly about lost revenue and dropping media sales. If they can recoup some of their invenstment in other manners (like charging companies to put ads on the DVDs) they will jump at the opportunity.
We will soon see ads on DVDs. It's not if, it's when.