They also have this weird stiff-arm syndrome sometimes, both when standing in-game and during cutscenes. It looks like the animators forgot to do something with the arms, they just hang rigidly and slightly off to the sides instead of straight down in an actual neutral/natural/relaxed manner.
I hadn't noticed the posture being that bad with NPCs, though. Seemed to me like Cassandra, Leliana and Josephine (okay, she gets her own set of animations with the clipboard and pen, so she's a special case) were always standing/walking properly. Maybe the skinny PJs enhance the gorilla effect while armor masks it a bit.