transformers is essentially a kid's movie and they want the kids to be able to tell at a glance that the robot is 'female'. kids are stupid, so all the crap that you can't figure out why they need is to make the stupid kids feel less stupid by being able to follow the stupid movie. feminism doesn't really have a goddamn thing to do with it. if you're questioning the logic of a movie where giant robots come from a robot planet to wage their war - but are able to blend in to our society by turning into a bloody walkman - you have REALLY missed the fucking point.