It's NOT a t rip off if it's a passing similarity in a freaking teaser poster. Get uppity about it when they rip off the storyline, or one of the characters or something.
Until then, it's a homage. A homage of something that's popular right now so it gets instantly recognized. That's not "cheap", it's rather effin' common and done all the time.
Watchmen isn't even popular with the general populace, anyway. Not even after the movie. It's a geek phenomenon, the movie was not the mainstream success they were hoping.