The follow powers gain NO benefit from Armor Penetration:
Flamestrike
Divine Glow
Divine Searing Light (normal Searing Light is fine)
Daunting Light
Chains of Binding Light
Prophecy of Doom
Forgemaster's Flame DoT (initial damage is fine)
Break the Spirit DoT (initial damage is fine)
Brand of the Sun DoT (initial damage is fine)
I suppose most DC's haven't geared for Armor Penetration, but I expect they will as the new DC Feywild set includes it. I tested every At-Will, Encounter in both normal and divine mode, and Daily. Everything I didn't list is working correctly. Unless an exception is mentioned, both divine and normal versions are affected the same.
Relevant thread in the DC forum:
http://nw-forum.perfectworld.com/showthread.php?473031-Chains-can-crit-ArmorPen-and-Repurpose-Soul-broken-Help-me-test