Letting DoW have blunt weapons and slashing weapons would change your loadout requirements. You'd have to determine what type of damage a boss, say, would be more susceptible. And bring the right weapon to the fight. And bring the right team members to augment your major damage type.
Since "Blunt" and "Slashing" is probably just a characteristic in weapon coding, it probably wouldn't be much problem to allow PLD, WAR, DRK to carry and equip both types.
But it'd be interesting to see how team compositions and fight balance would change!