How the ESRB handles downloadable content

We've always been curious how the ESRB handles the rating of downloadable content, especially after the Ratatouille "Hobo Murder and Cleavage" DLC pack caused such a stir earlier this year. While speaking at the MI6 Conference last week ESRB president Patricia Vance explained, saying, "they have to keep the content in the downloadable product consistent with the core rating. It can't go out of bounds." Presumably, if content was bad enough the game would have to be entirely re-rated.

Here's what we find interesting: If a publisher wanted to release AO content, but were afraid that stores wouldn't carry it, could they wait until sales were on a downturn and then release the naughty DLC? Because if it has nudity or a way of murdering people we've never tried we are totally there.