The time requirement comes into effect, too. There are several more instances (Five currently, one more comming out next month) where you have even more things to manage, and if you fail, you can't try again for three days or a week, depending ont he reset times.
Anybody who calls WoW dumbed down needs to sit through the Razorgore fight, and keep in mind that there are three (soon to be four) dungeons worth of bosses that put Razorgore's twelve minutes of pure chaos to shame.
For reference: Razorgore is the first boss (For that matter, the first hostile NPC you encounter in BWL, no "trash" pulls leading in) in Black Wing Lair. He comes complete with roughly 80 assorted mobs by the end of the first half of the fight, many of which can oneshot anything that isn't in plate armor. You need to manage all of this crap at the same time, while keeping Razorgore alive so you can battle several orcs for control of him. You use him to destroy the dragon eggs and stop more crap from spawning all around you, clean out the immense hordes of orcs and dragonkin, and THEN you get into the actual two-phase fight against Razorgore himself, which would be nontrivial going in at 100%, let alone how much the first half of the battle takes out of a raid. One person fucks up, does something stupid, screws up kiting or even walks in the wrong place? You all die, incur a repair bill tha can top 5 gold for warriors. You can't run away, the gates close behind you and the door in front of you leads to an even harder fight.
This fight is not a matter of having good gear - drops from much, much harder fights do not trivialize Razorgore yet, and it's doable with less gear than is needed in the lower level raid Molten Core - it's not a matter of grinding or farming. It's a matter of reflexes, practice, and just pure dumb luck most of the time.
I've heard a lot of people suggest WoW is "dumbed down." I've yet to meet somebody who will say that after they've done a Tribute run in Dire Maul North, done the Warlords Command quest, or even attempted (Much less succeeded) in the Baron's Ultimatum. Reducing the player cap in endgame dungeons from 10 to 5 has already made the end game impressively difficult. The final bosses in most endgame dungeons are now a challenge that's hardly reflected in the loot they give.