All in all the idea is that playing a Holy Paladin in raids isn't fun:
the gearing is really simple (spell power, int, crit, and nothing else matters),
the gameplay is simplistic (Holy Light spam, ehre you come),
the mobility & raid healing is very limited.
Though I'm playing a Holy Paladin for a good number of months now (was prot before WotLK), I do agree that, compared to a priest, the gameplay of a paladin is very limited. We are healing powerhouses, mana batteries and can outlast nearly all other healers. But we are not very fun to play ... and that's a very important issue in a game.
We have some plans for Holy paladins in 3.2. We'll talk more about them when we get closer and we are more confident that they are the actual changes that will go live (modulo PTR feedback).Let's hope they're going to find a new direction for us that can bring a bit more variety to our gameplay, that would be really sweet.