Blizzard has decided to make some adjustments to tank survivability in preparation for upcoming Heroic attempts in Icecrown Citadel, which has resulted in a paladin nerf and a death knight buff. Here's the details from Crygil's post:

Paladin:

• Sacred Duty now provides 2 / 4% Stamina, down from 4 / 8% Stamina. The cooldown advantages of the talent remain unchanged.

Death Knight:

• Frost Presence now provides 8% Stamina, up from 6% Stamina.
• Icebound Fortitude now provides 30% base damage reduction, up from 20% damage reduction. For a geared tank with high defense, this translates to 50% damage reduction, up from 40%.

"It’s important to note that we aren’t trying to single out paladins here," Crygil said. Blizzard decided this made more sense than buffing warriors, death knights and druids and then increasing boss damage accordingly.You can discuss the changes in this thread in our WoW general forum.