@Dom
People ARE misunderstanding how raids work now. BC and Vanilla raids were DOMINATED by guilds. LK? not so much. Where you do have the strong guilds still mopping up the average raid, I see a disturbing amount of PuGs on my server. SUCCESSFUL PuGs. The truth of the matter is the game has moved away from the elitest theory of "guild or go home." WoW has tried to bring in more casual players with this expansion. With casual players, more PuG raids are formed.
That being said you are thinking in a GUILD mentality, but a lot of us are thinking of PuG mentality. The raid leader doesn't care if you know why blood elves are paladins or why there are orcs in Azeroth. All he/she cares about is how fast you can down a boss so people can get their gear and badges and move on.
Blizz should rename their new slogan "Bring players, not the class." The don't care about THE players just players in general. Bring the accounts, not the class. That may be appropriate. When you can pick any of the 4 tanks and all of them can tank a raid but 3 can do it easier or with significantly higher DPS, the fourth gets passed over a lot.

So maybe everyone in the game seems to have a wrong idea of raiding, but planning takes time outside of raids. I don't know about you, but I've only seen one PuG start up a day or two before they run it. So bliz isn't going to waste time on making a "guild only" raid that follows a "Traditional" raid mentality when they are trying to bring in all the casuals that they can. Raids are over glorified 5 mans now. Niche toons like warriors, are not surviving.