Maybe it's because hybrids have a mana penalty!?! Their spells cost more mana casting than what is stated on the spell. This is not the issue with pure casters. Maybe it's a way to help the hybrids :o)
Well if you notice the old ways of VI it was to give the melee hybrids decent ac but very little toward int/wis. Maybe they finally put a tad bit of thought into the creation of the items.