Well, I don't agree. Going to the Raid/Dungeon thread to discuss healing in general feels like a bad idea. You can not assume that a player is ONLY into 1 specc anymore. Most people have multiple alts (I got many healers, all classes/speccs) so I feel many are viable to discuss healing, not only by class.
Blizzard Forums have this, and I think it works great. I see many times that different classes can give eachother a lot of feedback constructivly, both negative and positive.