I havent seen most of the Saw films as the Jigsaw concept just doesnt appeal to me and the acting and script in the films I saw were just atrocious...
That said...I hate to be the defender of torture porn...but these movies DO have a place in horror, and in theaters.
What most people dont realize (including the films own directors and production teams) is that Jason, Freddy etc are the HEROES of their films. No one is scared of Jason. If there was a real Jason, he'd be shot by a neighbor and the movie would be over. People like those films BECAUSE the killer kills people they want to see die. The egotistical jock, the cool black friend...even the virgin and her understanding boyfriend. We WANT them to die, and we watch these films in hopes of seeing the killer come up with new and cool ways of administering death. More often than not, these films dont satisfy that hope, as we get stab, stab, broken neck, stab time after time. That's why people still remember the good kills, such as Jason's sleeping bag assault.
Torture porn films deliver the goods. People can watch a series of pretty meaningless, but creative kills and then afterward talk about how awesome their favorite kill was with their friends, and then forget the movie ever existed. I think the reason for the public's boredom with Saw is that it is trying to provide a complex story, but most people don't remember the films details the day after seeing it, therefore the returning characters that should resonate with the public fall flat. I actually think the yearly format is what has saved the series, as other like Hostel have been forgotten. The point is, if you are going to try to deliver a story, itd better be darn compelling, and most people dont seem to really care about this franchise's story or anyone in it.
All that said, I do believe that it is quite possible to make a great horror movie in the torture porn genre. I just dont think anyone has ever done it.