According to a post by Zarhym, Blizzard will be boosting the armor on the gloves and chest pieces of the tier-10 plate tanking sets in the next minor patch in order to make them more desirable. If you're a warrior, death knight or paladin who just worked to get comparable gear, don't worry:

"Similar items crafted or purchased with Emblems of Frost will continue to be very good and will compare favorably to all but the Heroic difficulty boss loot, so you shouldn't despair if you recently acquired any of those."

Zarhym also stated later in the thread that they will be keeping an eye on Feral druid tank gear since they're concerned it won't scale as well.