If I may add my two cents....
I think that the debate of AOE tanking is interesting...., but the problem isn't that Paladins (or DK's) are better at it. They were in The Burning Crusade too. We weren't particularly upset about that then. This was, in fact, pre-shockwave and before cleave glyphs.
The real issue is the AMOUNT of AOE tanking that is happening now. In TBC, it was cool that some tanks worked better for some events. It made guilds show versatility and made you develop tanks of all classes. Who can forget that a Druid was better on Tidewalker or that Pally's were invaluable in TK for the birds next to Alar? There was creativity then.... and now there really isnt. Could you imagine a Paladin at level 70 running into the first wave of trash pulls in SSC and AOE tanking them?? They would have been dead in less than 10 seconds.
The problem isnt that AOE is easier for a Paladin or DK.... its that there is SO MUCH AOE tanking that it has relegated the less optimal AOE tanks to novelty. Im not saying you should have to mark up every trash pull like we did in SSC or TK, but AOE tanking is the difference between a 3 hour full Naxx clear and a 5 hour full Naxx clear. It shouldnt be this easy.
I beg Blizzard.... DONT make the tanks all the same. As a warrior tank, I understood when other roles were better.... whether it was a druid, paladin or even a warlock. Just make it so that any tanking class will offer a strength and weakness and make those advantages (or disadvantages) equally as beneficial (or uncomfortable).
Just one tanks thoughts.