For good horror movies you've nearly always got to look at the low budget,indie screne.
Sure Hollywood get's it right now & again (Exorcist,Omen,Shining) but the likes of Nightmare On Elm Street,Hellraiser,Evil Dead,Chainsaw Massacre,Halloween and even more recently Saw were (or near to) low budgeted independent movies.
Guess it's down to horror relying more on a creative vision then quality acting and the studios get too involved in the creative process.