Armory ranks 2s/3s

Hello everyone, i m here with the question: Why we have a common arena ranking between Frostmourne(which actually uses 3.1 patch, and don't have acces to end gear pvp/pve) and Icecrown, Blackrock and Lordareon,? My suggestion is for Frostmourne to have their own armory rank, while Blackrock, Icecrown and Lordareon another one. There are only 4-5 teams from the realms with end gear acces in whole armory, and i can't understand the ideea: Why should have a common armory with Frostmourne if we can't face them in 2s/3s arena?