See now, I don't see Misery as a horror movie. It's more of a demented drama. Maximum Overdrive is sci-fi as a meteor causes machines to become aware. Christine is horror as the car has a mind of its own and it's not explained. "IT" is the definition of horror.
Misery isn't horror as much as Stephen King's Stand By Me and The Green Mile are horror. Or even The Shawshank Redemption.