I have read through this topic, and many bring up valid points for both sides of the argument. Because I believe it is so, this topic has no clear black/white answer.
a) I'm an adult, so I have no need or interest in looking at ratings. Heck, I don't even know what the ratings are of the games I play (I could guess, but I never check or pay attention). I believe most gamers today are actually adults over 18.
b) Games are mainly sold on content and/or hype. CoD, GTA, Halo etc. are immune to ratings, in which I believe they would sell exactly the same were they rated 12, 16, 18 or 3 (I'm European) or E, T, MA in the US.
c) Some games would never profit from higher ratings. It's not like LEGO, Cars, Barbie or Hello Kitty would see a sudden increase in sales if they slap a higher age rating on it.
d) Only games that actually can see any profit from M rating are smaller exposure games with borderline content (to mind come Killer is Dead, Lollipop Chainsaw, Onechanbara - I must admit I have no idea what their ratings are) that try to entice teens to buy them by promising more adult content than those types of games usually have.
Also, I believe that this is much more of an American problem, because from what I've experienced, heard and read, Americans are much stricter in enforcing censorship and ratings.
And, I must also agree with one person above, to me it is still inexplicable that the noton is that nudity and sex will cause a much bigger damage to a teen's psyche than guns, blood and murder. Not only games, it's mainly TV where CSI is an early evening teen-allowed show, but Californication is adults-only late night show.
Make love not war, people.
