For the most part that held true with the first movie. The violence wasn't anything over the top, the swearing was easy to overlook and the sex was almost non-existent. However, halfway through the movie one character blurts out something that brought the theater to a standstill. Sam's mother asks him "Were you masturbating?" when she walks in on him after he was frantically trying to find something for the Autobots just outside his window. I know a handful of parents who had to have THE talk with their children that night, a bit a head of schedule, all due to that one line.
With the sequel, you'd think they'd have learned their lesson. Nope. In fact they do quite the opposite. Among the offenses in Revenge of the Fallen are a pair of Autobot twins that keep calling each other pussies and threaten to bust a cap in each others' asses, dogs humping dogs, robots humping humans, a fleeting but naughty shot up a college freshman's skirt, and a five minute sequence where Sam's mom downs a bag of marijuana brownies and runs around campus stoned off her gourd.
I'd like to hear how non-hippie parents explained to their kids why when Mrs. Witwicky used drugs, she just got really happy, but that it's a bad thing and they should just say no.
Obviously a PG-13 rating is supposed to imply that you might not want to take the kids. For example, the last two James Bond movies were clearly not kid friendly. But when a movie is based on a saturday morning cartoon and a line of toys, I think the expectation that it won't be that bad for kids is certainly justified.
Other filmmakers have at least taken this into consideration, especially with comic book based movies. For example, Batman is a comic that's been written as everything from a campy, kid friendly funnybook to a dark brooding tale of street violence. With The Dark Knight, filmmakers clearly opted for the latter interpretation, but they also knew parents would be taking the family to see it. So, despite the fact that over the course of the movie, people are shot, blown up, sliced open and in once instance, burned alive, this stuff is implied, instead of being seen. In fact, I didn't even realize that the guy got burned alive until the third time I saw it. They probably could have shown some of this stuff onscreen and kept the PG-13 rating, but they clearly understood that just because they could get away with it, doesn't mean they should do it.
Then there's films like Harry Potter and Star Wars, both of which had PG-13 installments in an otherwise PG rated franchise. These movies didn't use the more adult rating to give the films a bawdier twist, but instead it was just a heads up that the story was a bit darker than it was in previous installments.
In addition, parents weren't caught off guard by the level of violence in Dark Knight. Anybody who saw the trailer, or even just Heath Ledger's Joker makeup understood that this was going to be a dark and violent take on the franchise. As for people who saw the Transformers trailer, they just saw big robots fighting, not little robots humping things.
I'm not trying to sound like a prude or anything. I'm all for directors seeing their vision through to the end. I was all for Warner Brothers releasing the unrated version of Eyes Wide Shut because of how awkwardly censored the R-rated version was. When it was announced that Live Free or Die Hard would be PG-13, I was among the masses demanding to know why a film franchise for adults got taken down a notch.
But Transformers? Come on. Keep it family friendly if you want to sell they toys.