A lot of people seem to misunderstand how the DPS works from weapons. I've been volunteered to try to clear it up.
Weapon DPS is only cumulative for the hand weapon slots (e.g. dual wielding as an Assassin). The hand and ranged slots are mutually exclusive when it comes to damage.
Which slot/s are used to calculate the damage and which type of damage is inflicted are actually decided by the spell/ability more so than the weapon.
When you do a ranged/magic ability only the DPS from the weapon in the ranged slot applies.
When you do a melee ability only the DPS from the weapons in your hand slots applies.
If you look at it this is why Jolt currently behaves the way it does. Since it inflicts melee damage it's actually using the hand weapons for damage.
Warriors can only successfully use their throwing weapon with Jolt, which, ironically, requires a throwing weapon but doesn't actually use the throwing weapon(durability decreases on equipped melee weapons and not the throwing weapon).
Just making a staff do spell damage wouldn't actually change anything. The melee attacks/spells specifically do: DPS from your staff & DPS from your Melee attribute. At the same time the direct damage from the weapon in your hands does not get added to your magic and ranged attacks/spells.
The opposite is also true for the a melee build in most cases. Their ranged weapon damage isn't getting added into their melee attacks/spells. Nor is the average magic/ranged attack doing melee damage (Jolt being the odd case).
I have never seen a response by staff as to why they have not done this.
The answer is that basically that there is really no advantage to be gained from it.