Other than the almighty Poltergeist (my life... for you...), name me one PG-13 horror movie that was actually scary. Go ahead, I'll wait while you ponder that. Oh, and The Gate doesn't count, it wasn't scary at all, just freaky.
Got one in mind? Exactly. There aren't any PG-13 movies that are scary. No such beast, especially now that PG-13 horror is even more geared to the kids than Disneyland.
The Texas Chainsaw Massacre (original) and Halloween (original) both proved that you don't have to have blood by the gallon to be scary... but it helps when you're not restricted by the mediocre kiddie rating.
If I'm wrong, and this movie doesn't suck somehow, I'll be the first to admit it. But I'm expecting a stinker in the vein of Prom Night and When a Stranger Calls.