With solid confirmation that Naxx will be "floating" off to Northrend (and not exist in two places at once) also comes a strong hint by Bornakk that they will be removing the ability to get Tier-3 armor pieces along with the rest of the current Naxx loot. Bornakk says that "For players who want the look and the stats of tier 3 armor at level 80, hopefully they are already farming the dungeon for them." This is a very strong indication that post WotLK, the current Tier 3 gear will be no longer available.
Before today it has been pure speculation that this removal of loot would or would not happen. The only time that the WoW Insider staff can think of this happening before (save for the holiday and special events) is with a few old mount models getting changed. And that is nothing compared to entire loot tables being removed from the game. Note that the changes in patch 2.3 to old world loot were just that – changes, not removal.
In many ways this removal does make since, given that the armor models will be reused in Wrath of the Lich King's version of Naxx. While there is similar looking and colored gear floating around WoW, none of it is really twenty levels apart and powerful each in their own right.
However with that said, the removal of items from the game like this stirs a mixed reaction in me.