User blog comment:Emptylord/Season 3 - PBE Patch Notes/@comment-181.160.192.94-20121111055402/@comment-3974211-20121111132205

I think the main problem with Frozen Heart is that it's the highest armor and a massive reduction to your attack speed. Buying it completely counters an AD. Same issue with Force of Nature (kinda of, particularly when combined with the healing-triforce of Warmogs and Spirit Visage)... health and magic resistance counters most APs (health versus APs is stronger than health versus ADs, after all).