Out of curiosity, why aren't they using magic? Surely that could produce results as well. Heck, use blood magic.
The dudes in the pyramid head inspired armors aren't mages. If the demo is anything to go by, Redcliffe has many demons and pyramid head dudes, but only a handful of mages.
I'd also suggest that magic would be no more effective at torturing someone than normal means. A fireball might be flashy but I doubt it's any more painful than shoving a hot poker in someone's anus, or more frightening than dunking their head in water and holding it down until they almost drown.
If you're actually interested in extracting information, the best way of doing so is simply giving them only enough food and water to survive, not letting them sleep, and waiting.
While it is true that we see run-of-the mill torture implements strewn about, I don't think that necessarily rules out the possibility that magic may have been used to torture Leliana. Maybe the torture tools were plan B, after she had resisted previous efforts to break her. She does look rather clean for instance. (not bruised or bloodied & still fully clothed)
Having a scene where Leliana is half-naked and horribly blooded/bruised is probably something they'd avoid. Not to mention that you'd need a model just for that scene.