It's easy for gamers to understand the ratings system and what it stands for. However, you'd be surprised how many adults disregard it for the silliest reasons, or just how much they freak out over it when you do explain the context. Very rarely do you find parents that look at it the same way they would a movie's rating. Often, after you explain a game's content as they're preparing to purchase it for their ten or twelve year old child, they'll say "so what?" as if you're wasting their time, or they'll freak out and say ignorant things like "no wonder our kids are so violent and doing drugs!", etc.
The only real comfort that can be found is that comics went through a similar growing pain, only they actually had even more ridiculous restrictions.