The MPAA is so hypocritical about the line between PG-13 and R though. Fifteen years ago any sort of decapitation would get you an R; now they're fine for PG-13. Same for scenes showing people getting shot in the head. Titanic's frontal-boobs scene with Kate Winslet would've been R in any universe, and it would be today, but James Cameron is special and can achieve whatever rating he wants....yet two brief shots of George Clooney's butt meant that Solaris was originally rated R, but had to be appealed to PG-13.
And how many people get killed/maimed in the average PG-13 disaster movie? Is it just the presence of blood that merits an R? Or is it just the ratings boards' mood on the day that they screen it?