Originally Posted by
Shandalay
I'm not sure if this actually means anything, but the forces moving into Darkshore from the North, which are Saurfang's forces and are made of trolls, tauren and orcs, do take prisoners. From what the prisoners are saying they are civilians, not military, living in Darkshore and you can free them in the world quest. So Saurfang does seem to want to make this victory a clean one in the sense of fighting mainly military, and capturing civilians instead of killing.
I know that Malfurion isn't a civilian in that case, but I could imagine that Saurfang knows that Malfurion has some significance for the world as a whole and he simply has a moment of doubt when he is supposed to kill him, if this is actually something he should do for 'the good of the Horde'.