QUOTE(DemonEyesBob @ Jun 15 2011, 11:57)

Not completely true. That is how it has been recently, but several patches ago Penetrated Armor would also decrease monster barrier rating (magic defense). So you could use a rapier and battlecaster armor and cast ridiculously devastating spells.
Ahh forgot about that, I used that very late then it was removed, I cried a little inside.