My best guess as to why they didn't code them the same as regular weapons is because they change damage dice.  I doubt that in its current form that the code can support weapons that change like that.  So as a workaround, they made the unarmed damage based off of feats, and coded the handwraps to enchant the player directly, which is why you see the stats of the handwraps on the player when you examine them.  This made coding of handwrap damage as simple as counting the number of unarmed damage enhancement feats you have (including stuff like past lives and equipment) and referencing an entry in their database that would set the base unarmed damage level. 

This is probably also why they changed what the Ram's Might spell does in DDO, in D&D it directly increases the size category of the weapon, and I doubt that this would work in DDO's current form.

Just spitballin, but I would guess I am not too far off the mark.