Please take a look at my answer on [this post](http://gaming.stackexchange.com/questions/85258/how-does-the-skill-damage-work/85799#85799).  

 It explains the skill damage and it comes down to the point where your righthand weapon dps is used aswell as a slight bonus if the offhand is a weapon and no bonus if the offhand is a shield (before taking any dual-wield modifiers/skills etc. in consideration).