Hmm, I also thought of that. Maybe assassins have a one-shot bonus or some crits and more damage. There was actually only one dagger equipped. Even after I wore the sword, I could see a TWO-dagger wielding sprite. I didn't check with another kind of weapon to see if the daggers are actually fixed and not the image of what you're equipping. Maybe even if you wear a hammer you can see two swords.
And yeah, it looks pretty baddass :3 I've always liked the dark assassin aesthetics.