Movies go through a lot of changes from the original concept to the finished product. For those that become big hits or go on to become classics, those changes are mostly for the better. Only years afterward do we find out what could have been -and by then the early ideas seem just plain bad.
Let's just be glad these horror films turned out the way they did -mainly because we can't imagine them as anything else. See how your favorite horror movie could have been very different in a pictofacts list at Cracked.