There's an interesting article on Hollywood and its lack of original story lines in feature films. This is explained quite simply; movies cost a lot of money to make, and studios don't like taking a gamble on a new idea. Thus, we're left with a constant stream of sequels and adaptations.
Although most of us dream of making a feature film one day, maybe we should change our feelings on what many of us perceive as a limitation and embrace the short film. Someone once told me that true artistic freedom lies in film school; you're free to dream up any idea and make it on your own terms. Make your short film with that in mind and chances are that short will be more creative and original than what you see on the big screen.