I'd be interested in hearing what you feel is the difference as they seem rather similar to me, or rather more of a difference between high-brow horror (e.g. the Shining) and low-brow horror (e.g. Friday the 13th). So I suppose it is more of a spectrum.
Of course Theon Greyjoy might feel differently.
Theon is an interesting example to choose - you mean what happens in the books, right, where it is
entirely off-screen, where we see and hear nothing, not the show, where it's graphic and lurid and actually kind of horror-funny? Because the books are definitely not torture-porn, given we don't even know about until long, long after it's happened, for the most part. The whole point of the term "torture porn" is that it is graphic and so on, that it is supposed to thrill the audience, not just horrify them (e.g.
Saw,
Hostel, etc.)
SoT, as Thaum says, is excited and really "into" the torture and so on, to the point where it's barely horror, and it has extremely disturbing psycho-sexual stuff - for example, Richard is tortured (in a totally non-disfiguring, non-soul-destroying way, of course) by some sort of sexy bondage-nun, who later (IIRC), begs him to kill her, whilst she is lying on a bed, and then he uses his magic sword in it's "special mode" (I swear to god this is literally what happens not a weird euphemism except it obviously is VERY WEIRD AND CREEPY and not in a good intentional way because the author seems to be suggesting it's totally cool) to kill her. Generally we're asked to see horror and carnage as exciting - in one of the later books Richard chops his way through unarmed, not-real-threat civilians (admittedly brainwashed, but they're a human shield), and we're clearly, from the writing, meant to think it's totally rocking that he's choppin' up these commie bastards (even though they're brainwashed...), not that this is a sickening scene of violence as an armed, armoured, magic-sword-wielding unstoppable wizard kills unarmed civilians.
It's not a high-brow/low-brow thing, either - GoT and SoT are entirely different genres. GoT is extreme multi-pov epic fantasy focusing on intrigue and politics and the nasty consequences thereof, with a bit of an apocalyptic magic threat in the background. It's certainly Dark Fantasy. Whereas SoT is simple "Man gets ever more powerful"
High Fantasy, the only real flair to which is that it was creepy psuedo-BDSM psycho-sexual stuff (which real BDSM lifestylers are not at all keen on, I understand), and that it is explicitly (as the author has explained) political propaganda in service of Objectivism, a philosophy which is to Libertarianism as Maoism is to, say, basic Marxist Communism - which is to say a weird cult-ish offshoot which doesn't make much sense and is basically a religion/cult-of-personality. That's beside the point here, though, which is that SoT is very keen to get off on how awesome ultra-violence is, and uses torture for cheap thrills.
I can't really comment on The Shining vs Friday the 13th, except to say they are perhaps poor comparisons, because whilst Friday the 13th is lower-brow in the sense of having less to say (but not a lot less - The Shining has little to say either), I think it's quite a lot more successful as a film and rather more impressive as a piece of film-making (I love The Shining, but it's a flawed flawed thing) than the former.