From Sylan of Gilneas, on the WoW paladin forums:
Lore changes. Evolves.
After Uther died Paladins lost their confidence. Paladins realized that they were mortal. Vulnerable. This fear has pervaded since Uther's demise and shows up in every aspect of the Paladin class to this very day. In fact, Paladins are so shaken that even their god-mode bubbles have begun to falter. At first Paladin lost their ability to use both bubbles back to back but as time went on things got worse. Priest learned of how shaken the Paladin faith was and learned to twist their magic to the point that they are now able to completely remove the god-mode bubble.
It is rumored that Uther's death may also cause Paladins to lose some of their ability to regenerate mana.
It's all in the lore if you know where to look.
Wow. That explains so much!