I think the whole rating system is rather broken myself. At times about the only difference between PG-13 and R has seemed to be a lack of showing the whole boob, an excessive amount of blood, and dropping the F bomb more than once. But I can totally understand why the studio has been shooting for a PG-13 rating because it's an insane budget on these films so it takes a lot of tickets to make a profit at the movie theater and set up that revenue stream once the home release drops.
I disagree there is a clear difference between pg 13 and R the violence in Pg 13 is brutal but usually quick most Pg 13's don't allow blood period. Look at the Dark Knight compared to Watchmen. A clear difference going on there. Kingsman has heads blowing up and the church massacre neither of which would ever be allowed in Pg 13 movie. There are other examples but I think that shows enough to be clear. Also the movies can get away with the violence because it's mostly robot violence so what would normally be a heavy R rating is not Transformers has always been like that Beast Machines and Prime could be downright horrifying in what they showed. Beast Wars blew characters to pieces. Even G1 had some violent stuff Optimus was torn to pieces by Megatron and left as a sentient severed head while the rest of his pieces were used in a near Frankenstein manner, I mean damn!
A notion that Revenge of the Fallen took faaaar to literally. Comics have always, always been a different beast to the cartoons of the day and truthfully, what was in them was probably on par with other Marvel comics. Not a criticism, everyone I talk to about the G1 Marvel comics sings their praises, just an oberservation. The animated movie is the exception to the rule with the G1 cartoon; the show propper both before and after was never to the same quality much to my dismay. There were some genuinely good episodes, but visually the movie remains the high point. And poop jokes are hardly new to children's television. They still had to bend a bit: Spectre General, strictly speaking, don't exist. The band's actual name was Kick-Axe and most of the tracks would qualify probably as hair metal: awesome hair metal but hair metal none the less. Indeed; and all those epic duels to the death in the film were written in for that sole reason. Clear the character slate of old toys for new toys. We have different definitions of awesome. The rating works since it covers all the bases.
Pg 13 is the perfect rating market wise for almost anything really because naturally parents don't want to take their kids to an R however some might find PG movies to be too childish. PG 13 may as well have it's meaning changed as it pretty much means a movie that will have some mature topics for older audiences but won't be too intense for younger audience either. Basically it means this movie is aimed at all audiences.