Again, parents censoring things is acceptable. The industry coming up with regulation standards, I believe, is not. I remember reading (and seeing other kids reading) Amy Tan, Tom Clancy, and John Grisham novels in early middle school. We didn't necessarily understand all the concepts inside the novels, but it still influenced us.

Could you imagine all the books intended for teens and tweens with controversial content suddenly being "rated" more mature simply because they deal with sexuality and religion (first example to come to mind: Are You There God? It's Me Margaret)? Regulation standards lend perceivably objective weight to a completely subjective standard.