Protectors of Moonglow

Raids & Dungeons - Hard Mode
Ulduar has a ton of bosses. While I'm sure some players would love for us to deliver an instance with that level of content every month or so (and throw in a 5-player run to boot!), it's not in the cards, at least not for the next couple of years.

Instead, what we tried to do with Ulduar is offer a lot of different ways to play the encounters. While the progress-oriented guilds may clear it quickly, we hope that some of the hard modes will offer them a lot to chew on. All of the players who are somewhere between barely being able to clear the instance and the "world first" crowd should be able to find a comfortable difficulty level as well.

Your old model towards end game was a success, it brought you eleven million players.
Most of whom never had a chance to finish a raid. They didn't get to see some of the best art in the game, hear the unique music or voice over, or in many cases even see the villian at the end of their quest line. From a production POV, instances are very expensive. It seems an odd choice to lavish all that attention on such a tiny percent of the player base.

At the same time, we know there are players who love a challenge and are willing to do almost anything to beat a raid-destroying boss provided they also have a shot at the best loot. They don't want the instances to be over too soon. They like banging their head against the wall.

And so hard modes were born. We tested the water a little with Obsidian Sanctum. We're going full bore with Ulduar. (Source)

Ulduar - Difficulty
We had to fix some problems, and very rapid mana regeneration was one of them. Another big one was amazing tank cooldowns (mostly from the DK). However we stepped up the difficulty on the encounters too. There is no “just burn him down” boss like Noth. The trash will require crowd control on some pulls. Ulduar is not Sunwell. It is not a huge leap up in difficulty from Naxx, but it is a step up. If that isn’t enough of a challenge for you, then I suggest you try the hard modes and pay a visit to Algalon. (Source)

Healers
They should not be running out of mana in Ulduar if they play well. In Naxx you can do things like stand in fires, overheal like mad, bring players in green gear to get geared up, or not even explain the fights to pugs because you can brute force your way through them. One the mechanics that allows you to brute force is having so much mana regen. Now all of that is appropriate for the first raid tier. Things will start to get a little more difficult now, and a lot more difficult if you want to do the hardest fights. Naxx = play bad and win. Ulduar = play good and win. (Source)

Ulduar - Hard Modes
Hard modes are designed to give very skilled groups something to do while still allowing more casual groups to see the content. Ulduar has 14 bosses. We haven't done an instance of that size since the original Naxxramas, and Ulduar has a lot more unique content than Naxx had. You are imagining a world in which if we had not done hard modes, you would have gotten another entire raid. That is a bad assumption. You would have gotten Ulduar, cleared it quickly, and then been bored again.