Relmstein has been doing an excellent examination of the two seemingly strongest forces in the Arenas-- Paladins and Warriors. His second column probably should have come first-- he did a breakdown of Paladin and Warrior numbers on some of the top teams in the Arenas, and as you might have expected, they're out there. Out of the twenty teams he looked at (the top five teams on four different battlegroups), 15 had at least one Paladin and one Warrior, and 18 had at least one Paladin or one Warrior. One top team (Pretty Standard on Stormstrike) even has one Paladin and three Warriors-- two Arms, and one Fury.
So now back to Relmstein's first post on the subject-- what's the deal here? Arena is singular among most of WoW's PvP in that it isn't about capturing flags or nodes or completing objectives or earning points for your team. It's all about staying alive. And no one does that better than Paladins and Warriors. Combine that with the fact that both classes have amazing talents for either keeping others alive (Paladins can heal and stay alive), or negating the opponents' attempts to stay alive (Warriors can stay alive and do Mortal Strike), and you can see why Warriors and Paladins are so valued in the Arenas.
This doesn't mean Warriors and Paladins are unbeatable-- a Paladin needs mana, and a Warrior can be counteracted by crowd control like fear and Hunter traps-- but it does make the classes tailor made for getting in fights and remaining upright at the end. Blizzard has already said that they're fine with letting certain classes be stronger in some areas than others, so it seems, as Relmstein says, that in Arenas, the Arcanite Reaper days are back. Beware Mortal Strike and the Paladin healer in the Arenas.