No, but it's been happening with a lot of people, to the point that if it's crappy, it will sell millions.
No one buys games based on their ratings. Certain games have been stuck with a much higher ESRB rating than they should (Halo is a prime example) and other games aim for a lower rating for a broader audience (like Red Steel 2 cut the blood and gore for a T rating, despite you still being able to shoot and slice people).
There's no prejudices on which games are "hardcore" or "casual" based on their ratings. It just so happens that in today's day and age, a lot of games are much more mature. Think of it like movies. A lot of movies are more "mature" and an overwhelming amount of releases are R rated. But that doesn't stop us hardcore movie goers from enjoying a Pixar flick like Toy Story 3 or the upcoming Brave. People my age are gonna run to the theaters for Abraham Lincoln: Vampire Hunter and rush home the next day to watch Legend of Korra on TV. Ratings are just ratings, they have no outward effect on a game.
Plus plenty of parents will bar certain games with notorious reputations (I couldn't buy Grand Theft Auto until I had access to my own debit card and stuff) or based on ratings.