Hypersmurf said:
Only useless if you have an enhancement bonus of less than +2 on the weapon.
And it's complicated by taking an implicit "minimum of +1" rule (explicit in the general Magic Weapons section, but not highlighted in the Ability description) and reminding the wielder of its existence.
I don't see it as less simple, and it strikes me as the natural consequence - if you transfer away a bonus that has benefits, you lose access to those benefits until you regain the bonus.
-Hyp.
But you aren't transfering the bonus
away from the weapon, the ability just allows you to utilize the bonus in a non-standard way. The enhancement bonus on shields increase the hardness and hp of the item in the exact same way as a weapon's enhancement bonus.
SRD said:
Defending
A defending weapon allows the wielder to transfer some or all of the sword’s enhancement bonus to his AC as a bonus that stacks with all others. As a free action, the wielder chooses how to allocate the weapon’s enhancement bonus at the start of his turn before using the weapon, and the effect to AC lasts until his next turn.
Notice the word "allocate". That implies that the weapon still has its enhancement bonus, just instead of allocating it to the normal purpose of providing a bonus to attack and damage, you can choose to allocate the bonus to your AC in a very specific way.
Interpreting it as the weapon "losing" it's enhancement bonus would be needlessly complex at my game table. It would make Defending the only ability that you can put on a weapon and not be able to use at all (in the case of a +1 defending weapon), a weapon could self destruct from shifting the bonus, hardness would vary up and down, and caster level would vary up and down. It would really mess with the new weapon crystals out of the Magic Item Compendium, since I believe some of them have a minimum enhancement bonus requirement for the weapon to which they are attached.
To prevent abuse (dual wielding defending weapons with defending armor spikes on both your armor and your animated shield), I would rule as a DM that the AC bonus from multiple defending weapons don't stack with each other (under the clause under stacking that indicates that unnamed bonuses from identically named sources don't stack), and would not require an attack to utilize the bonus to AC. If a character really wants to pay 72k gp for a +5 to AC (that can be easily disarmed no less) instead of paying the 50k gp for a +5 ring of protection or amulet of natural armor, or even 64k gp for +8 Bracers of Armor or a +5 moderate fortification buckler and still have money left over, I would let them.
I would also say that if you allocated the entire enhancement bonus to your AC, the weapon would not defeat DR #/Magic since the DR entry specifically says:
SRD said:
Some monsters are vulnerable to magic weapons. Any weapon with at least a +1 magical enhancement bonus on attack and damage rolls overcomes the damage reduction of these monsters.
If you have allocated the entire bonus to AC, that means you have allocated none of the bonus to attack and damage, and thus have not met the criteria to defeat the DR.