Spell buffs and gear bonuses used to cap out at the same bonus - +5.
Resistance (Nightshield), Natural Armor (Barkskin), Deflection (Shield of Faith)
Now with crazy stat inflation on current loot, you can get a +5 bonus to the above stats as early as level 7 with a Master Craftsmanship item. This is far earlier than it takes for the corresponding spells to cap and provide their full bonus and the gear bonus goes all the way up to +10 now.
What's the point of these buffs?
Would be nice if there were an appropriate increase in the cap and progression of these spells that mirrors the bonuses provided by gear. +1/2 caster levels, perhaps. This would keep pace with available gear nicely in the early game and provide a slight boost for the spell user in the mid-range levels.
After all, if magical items are created by an appropriate level caster imbuing these spells into an item, how do the bonuses from the items rise above what the spell is capable of producing?
While Mage Armor doesn't fit the same mold as the other spells, I think a case could be made for putting it on a similar progression. The static +4 bonus provided by Mage armor is very nearly useless even at level 1 where it's easy to find a +3 armor gear. (And +4 at level 3, making Mage Armor completely useless thereafter)
Personally, I would have preferred to keep the original spell progression and enchantment caps from the DnD source material, but that cat seems to have already escaped the bag.
It seems sensible to me that bonuses provided by spells, given the temporary nature of spells and their reliance on SP to be cast, should never be inferior to what's available on an enchanted piece of gear.