Well DCI is partly do to your combat skill. Parry is another matter all together. So if you are using a spell book with no wrestling or don't have Anat+Eval, you will totally get hit. Same with any dexer, Say you have fencing and holding a sword with no UBW, that's like having 0 skill. A mage weapon converts the skill into a combat skill, hence the dci bonus.
Archers do have a dci bonus, but no parry chance, not even holding a bow where as any other character holding a fence,sword,mace wep would get 1/2 their parry chance based on skill, for example if I had a char with no bushido and I had a 30% with a shield, I would have a 15% to block with a weapon.
Ok I am rambling..