I think I found where all the priests and druids went. I joined a group for Tempest Keep - Arcatraz. We had one priest and two druids. Guess who ended up main-healing?
It was still a good and successful run. And I got to play with a Shadow priest for the first time in TBC. Shadow priests really complement Holy Paladins, to an almost rediculous degree. All that extra mana fueled my larger heals, and the group healing through Vampiric Embrace took care of all the splash damage that makes paladin healing hard.
In many ways, Shadow priests are the one hybrid that Blizzard really got right. Unlike a paladin, a Shadow priest does not choose between healing and doing damage. They heal by doing damage. Vampiric Embrace is the critical talent that makes the Shadow priest work. And the amount healed is linked to the amount of damage done, which gives large incentive to maximize damage capabilities.
What a lot of paladins really want is our own Vampiric Embrace. (Angelic Embrace, maybe. Though Blizzard would probably call it something silly like Embrace of the Naaru.) Imagine a Retribution talent where you healed your party for a certain percentage of the damage that you do. That is the precise solution that would make many Retribution paladins happy, because it gives the extra, obvious purpose to their meleeing. We are a melee hybrid, and so we should support by meleeing.
Judgement of Light does not work as well as Vampiric Embrace because JoL is independent of the paladin. There is no support incentive for the Retribution paladin to maximize his damage in the same manner as the Shadow priest.
This solution to the paladin role is fairly obvious, and I think that is the reason that Blizzard has been resisting this. It's really too close to Vampiric Embrace, and I think that Blizzard does not want to just copy themselves. But I think all their other attempts have not truely restored the paladin class to the melee zone for the large majority of players.
But so long as casting a heal reduces your dps (which it does, as time spent casting takes away from time spent meleeing), I think paladins will always have this tension between being allowed on the front lines or being forced to healbot.