What sorts of movies make money?

I once spent a semester doing econometric analysis of what made some movies profitable and others not as a part time job. I liked it a lot, and if they’d been hiring when I graduated my life might be quiet different. One of the things at the time that struck me was that R rated movies seem to do worse than the more youth friendly pictures. Others seem to have found this fact with great robustness. A recent study in the book Holywood Economics found that not only do G rated movies they make more money on average, but that altering the product mix would result in higher studio profits.
A few questions come to mind:
1) Are good movie scripts around (unproduced) in all ratings? Maybe all the potentially good (that is not certain to be bad) G and R rated movies are made, so there just there aren’t more G movies to make profitably?
2) Since so many G rated movies are animated, is there something about the popularity or means of production of animated movies that limits how well it can be scaled?
Another finding is that cartoons seem to get gentler ratings than live action movies with the same behaviors. The ratings were far less stable than I would have guessed.
Here is a link to the top grossing movies by MPAA Rating.