(indicating some sort of direct damage reduction?)
Don't forget too, that we don't know the true stats for Monsters. We know they have defense, since Burning Metal lets you hit harder with melee. However there is also the possibility that certain monsters also have resistances just like players.
If monsters didn't have resistances, they magic would hit all mobs the same damage. That being said, Bears could easily have a Slash/Crush resistance to account for the reduced damage compared to other monsters of the same level.
Another thing to factor in is the "cap" of damage reduction on monsters. For example; Your defense has a cap on 2 things; Damage Reduction (from melee) and Crit Damage Reduction (from melee). Even if you reach your cap on Damage reduction, increasing defense can still increase Crit Damage Reduction to its cap.
So say, a bear is 10,000 defense, but capped at 10% damage reduction and crit damage reduction. 10,000 defense would be high enough to cap that damage reduction and crit damage reduction at 10%, but other mobs may not be the same. Mobs outside may only have 10% damage reduction and 6% crit damage reduction, adding for a variance in hits.
The cap could also be different on different mobs. I know the soldiers in Rage Cape take a significant more amount of physical damage to kill, compared to other monsters of the same level in the same dungeon. It is unclear if this difference in damage is due to reduction from defenses or actual physical resistances on monsters.