I am seriously surprised at the short sightedness in people who say "It's rated Pg 13, you should know better".
This is a movie based on a kids show that is marketed towards kids and people who AS KIDS grew up liking transformers. Most of the merchandise (i.e. toys) for this movie are in the same isle as the Star Wars, Bakugan, Ben 10 and Pokemon toys and in case you forget this is licensed by Hasbro, which is a toy company. Hell in my Target the Transformers stuff shares an isle with freaking Thomas the Train and Fisher Price Imaginext toys.
If you are not a parent I doubt you really care and the whole point is that there is no reason for YOU to care about the swearing. But parents (like me) who have two little boys that pretend each and every day that they are transformers and talk about transformers all day long and ask you questions like "Who do you think would be a better leader of the Decepticons, Starscream or Megatron?" and then proceed to tell you the pros and cons of each freaking character are the ones who want to take their kids to the movies to have an awesome, epic movie experience and we can't because of robots calling each other "pu**Y" and "bitch" which is completely and totally not needed.
*I* do not have a problem with foul language. Some of my favorite movies of all time are loaded with profanity like Scary Movie 1, 40 year old virgin, role models, etc. But they are not in any way marketing towards kids, with figures in the freaking toy isle and in Burger King kids meals.
Yeah the movie made $200 million dollars in the first week but anyone who went to a show before 7pm can tell you there were A LOT of kids in the theater. Parents are ok with letting their kids have some exposure to "fantasy violence" (look at all the weaponry and blasters and combat material in toy isles) but not so ok with cursing. It's the same thing with Star Wars and why it's wildly popular. But if Obi Wan was calling Anakin a whiny bitch and the Emperor was telling Luke he was "getting an ass whuppin" you suddenly change the game completely and you piss off a lot of parents (i.e buyers).
We buy the toys, clothes, posters, books and games for our kids and we take our kids to the movies. We are the reason Transfomers are successful today and our parents are the reason it was successful in the 80s because parents PAY for this stuff. Sure there are collectors but I'm not so sure Hasbro banks on collectors to fill their coffers around Christmas time and buy kids meals and wear transformers pajamas to bed.
So in a nutshell, parents don't like the language because we WANT to take our kids to the movie, but can't. Before anyone says "it doesn't matter what YOU want", well it certainly does matter because I don't know of anyone or any movie company aside from maybe Kevin Smith who makes movies for themselves.