Combat Mastery, Sword Mastery, and Lance Mastery are the next reforges you want, with the last one being out if you don't use Judgement Blade. They're added on to gloves, and will give 1 per level. Out of these, Combat Mastery is the best one for the reason you mentioned, but generally, dual reforge (or triple if you're extremely lucky) with Sword and Lance Mastery is preferred. I know Combat Mastery damage is added on to the "base damage" portion when it comes to dual wielding equation, and I just tested with NPC reforges, and saw that Sword Mastery damage reforge bonus doesn't double when I was dual wielding, which means that Sword Mastery Max Damage, along with other Mastery damages, would add to the "base damage".
Either ways, it's nice to have the best damage possible. And as for the OP's question of "what the hell is going on with that", well, that 10 more damage from an enchant is something you can't get if you have all your enchant slots occupied, so it's an ultimate way of getting more damages.