Over the last couple days I caught Saw and The Devil's Rejects on DVD and Hostel in the theater.
I've seen occasionally comments that Hostel, for example, is torture porn--oddly, not so much in reviews, even fairly respectable ones.
What these films have in common is advertising that pitches them as torture porn -- so intense (-ly gory) that you'll barely be able to watch them. I watched Saw first and was frankly surprised at how little gore there was (the Texas Chainsaw Massacre remake was the hardest endurance horror film for me to watch). The intensity of the film was mostly emotional--much more like Asian horror such as Audition or Old Boy. Saw kept the suspense on high through the whole picture and worked the best of my endruance horror week.
The torture porn label is inaccurate for these films not just because they're actually better put together than that -- but because it doesn't accurately describe the kind of emotion these films are trying to evoke.
The slashers of the 80s actually fit the horror-porn model better--typically they'd include some meandering scenes of attractive teeenagers, a short suspense build, then paid off the suspense with an inventive kill scene. We were meant to be entertained by the innovativeness, and perhaps even humor, of the method of the kill.
Saw and it's kind of film is very different, more endurance horror. They subject us early to horrible scenes of punishment, or take you right to the edge of seeing the mangling, and we're squirming in our seats, looking away from the screen, and maybe peeking through our fingers. It's like a Sour Patch Kid, hard to take but for some reason we're drawn to endure the flavor.
Unlike the slasher, the torture scene is not the payoff, it's the setup. We're thankful when the torture ends, but it doesn't end in a big scene. Instead the torture underlines the threat the main character faces in the remainder of the film. Later the suspense will be a lot more severe since we (the audience) desperately don't want to see the main character suffer, not only out of empathy but also simply because it's painful to us.