Someone with a lot more creativity (and time) than me put these together. I think someone else did a thread on common, annoying themes in movies like the guy walking towards the camera with shit blowing up in the background. Apparently there's even less creativity in movie posters.
Don't stop. Keep it going.
I wouldn't be surprised at all if the art for movie posters was based around research involving what is most likely to draw attention and elicit further interest depending on the target demographic, be it evolutionary psychology or simply trying to subtly force people into drawing first-impression parallels between a new movie and a previous successful one (e.g., if a popular movie had a particular cover, then a different movie with a similar picture layout would bring that popular movie to the individual's mind and potentially give him a warm and fuzzy feeling).
Or, with the thousands and thousands of movies out there, maybe there's just only so much shit you can do.
Or, maybe it's simply based on dumb trends... like the skinny jean phenomenon.
That being said, ain't nuthin' wrong with seeing a little female leg on a movie poster.
What about this one with all the comedies with big red letters. I can hear the announcer's voice in my head right now as he says the title with a stupid big grin.