With our recent story regarding Microsoft's Game Room only allowing games that would fall under E10+, we felt that people might be a little confused on how this actually works. So we spoke to the ESRB directly, and with it some more knowledge.
In regards to downloadable content for games already rated, if the DLC contains content that is in line with the original product's rating, it will extend to it. If it does not, like in the case of GTA: The Lost And The Damned, the content is required to be submitted to the ESRB for rating.
So as the Game Room is itself been rated E10+, all games that will be released for it will have to fall under the E10+ rating in order to get a free pass onto the Game Room.
E10+ does fit a lot of games, even those that most people would not expect - Streets Of Rage, Final Fight and other brawlers fit under the E10+ banner, probably due to the lack of blood.
There are very few games that fall within the Teen or Mature rating. On the Genesis there are a total of 18 games that were ever rated Teen or Mature including the Mortal Kombats and Golden Axe games.
However we may have been mistaken regarding one thing - games like Street Fighter and Mortal Kombat could make it to the Game Room, it's just that they would have to be rated outside of the Game Room for it to work. As we mentioned before - any DLC that fits outside the original guideline can still be a part of the game, but they'd have to be rated separately. A good example of this would be Lumines Live for the Xbox Live Arcade - the standard game is rated a standard E, but the Tokyo Club Mix Pack DLC had to be rated separately thanks to "Mild Suggestive Themes", and got an E10+.
BUt while it technically could happen, Microsoft are not interested in it at this moment. "We currently have no plans to feature titles of those [higher Teen and Mature] ratings", as per the previous article. But if we're going up the gaming evolutionary ladder with Game Room, we've got a long time before they even start thinking of emulating the Arcade boards those games titles work on, so don't worry about it.
As an added bonus, we also got the skinny on how music games like Rock Band and Guitar Hero work with their DLC. The way it officially works is that music DLC isn't rated either, but is requires to display the song's RIAA warning should it have one. Fascinating!
Hope that clears everything up.