Old discussion. Paladins are valid Tanks in any situation just as Warriors post BC. Some situations are better for Warriors/Druids, some for Paladins. That's a fact.

Though any can master ANY MT position if played and geared right.

Warriors have one or two more dmg migration skills and usually around 1000 more hp, but therefore Paladins can reach Uncrushable a little better due to Holy Shield. (making a properly equipped Paladin uncrushable as long as there are no more than 8 hits within 10 sec. opposed to the Warrior's Shield Block that makes the Warrior uncrush only for max. 2 Hits within 5 seconds, which can happen quite often especially if one attack is parried)

Also it is not just AOE Tanking with the Paladin. A Paladin mostly outthreats a Warrior therefore making a high DPS group more potent than a compared Warrior in his position.

Bosses as the Maiden are not exclusively, but better Tankable by a Warrior simply due to the silence effect that lowers the Paladin's threat generation. Also all sort of Spell-Shielded Mobs/Bosses are better Tanked by other classes.

Everyone got advantages and disadvantages in tanking, but all CAN MT in ANY Tanking encounter. Assuming anything else is ignorance and imo a little sign of inferiority complex if you do not want to be out of the spotlight if the situation calls for it.

In my Karazhan raid, we keep switching between MTing/OTing having a great team of a Warrior Tank and Paladin Tank (me). E.g. I would Tank Attumen&Midnight together and he would contribute a little DMG with some off gear. Then at the Maiden, I would decurse and throw in emergency heals and save people's asses with LOH if necessary while he would Tank. Also, e.g. I would Tank the Curator as my DMG output is quite nice (for a Tank) when tanking, and this shortens the fight a little. Sharing the spotlight is the key! Teamwork, people! Learn that!