Blizzard clearly didn't think so, as they buffed several hard mode encounters after they were first beaten, leaving the guilds who spent the first week banging their heads against them rather than racing towards Yogg-Saron wringing their hands in despair.
Part of the problem is how third-party sites treat hard modes and kills. When Ulduar was imminent, guilds shooting for world firsts had a choice as to what they killed, in what order, and at what difficulty. Part of the reasoning behind guilds' decisions included whether sites like GuildOx and WoWProgress would count achievements (i.e. hard modes) over normal kills - the guild listing on those two sites varies drastically, one favouring achievements, the other not. The decision by MMO-Champion, later reversed, to wipe the 'hard mode' hall of fame after Blizzard buffed the encounters also sapped some of the momentum from guilds trying to beat these versions of the fights.
Was Blizzard right to hotfix the encounters? Many players have reacted to this decision with anger and frustration, and perhaps it's right that changing encounters once they're live is a bad move. But having the encounters released in a state where guilds with practically no Ulduar gear, but plenty of time, could defeat them has caused bad moods among the hardcore.
The intended progression path during Ulduar is, theoretically, to clear normal mode before hard mode to gear up, only then attempting the more difficult achievements. Many guilds will do this, but since hard modes were available on PTR and players saw how feasible many of them were, several chose to attempt the hard modes straight off. Does this mean that they can complain when Blizzard changes the goalposts?
Since some of the hard modes have been beaten after being buffed, it seems that no matter how near-impossible Blizzard make things, guilds will still wipe relentlessly to defeat them before they should be able. Encounters do not seem to be intrinsically difficult, but hard due to numbers and flaws in execution - gear corrects the former, and hours of wiping the latter.
This might be a good time to segue into a misty-eyed longing for the glory days of old, but I'll resist.
Many raiders at high-end guilds enjoy wiping and throwing themselves against new challenges, but the general quality of those available has disappointed some. However, among the inhabitants of Ulduar there are several really interesting and challenging fights which are not only fun to learn but fun to beat; it just seems that the hardmodes have been slightly misplaced, and that is all some raiders care about.
Should the instance have been designed differently to avoid it being cleared in one week? There are a couple of different ways this could have been done, including resistance blocks (as we saw in Black Temple) and artificial gates (as we saw in Sunwell). In fact, Ulduar could have tenuously been linked to the Argent Tournament and we could have seen bosses uncovered as Tournament dailies got completed. Or there could have been a major frost resistance drive.
However, these artificial blocks don't satisfy hardcore raiders who are chomping at the bit, and generally give certain people a hard time - PuGs, those on low population servers, etc. An instance where everything is available from the get-go is certainly fairer, but if it leads to the hardcore raiding solidly for a week to kill as many hard modes as possible and still clear the instance, is it healthier?
We all know how the uber-hardcore treat new raid instances, and although such behaviour is a lifestyle choice, it's interesting to wonder whether designers do, or should, take the health of the hardcore on board. For example, the choice to limit playtime versus Algalon the Observer, which many believe to be the 'true' world first when it comes to Ulduar, means that raid guilds won't be able to break their backs trying to defeat him.
Instead, they will need to take an orderly approach, analysing tactics and perhaps even - gasp! - collaborating with other guilds to work out the best approach. With very limited time to put their moves into action (although this time limit will most likely be changed in future), raids will need to be sharp, focused and fast. We may even see a resurgence of things like wipe recovery and even repair bots, although Ulduar's teleportation system is likely to be enough for all but the ultimate min-maxers.
Should Yogg-Saron have been gated, or limited in time like Algalon; should hard modes have been unavailable for the first few weeks; or should other penalties have been invented to prevent guilds from pulling all-nighters to get world firsts? The answer to this question is obviously variable depending on your point of view. Yogg-Saron seems fine as he is, a nice encounter that's a great reward for the drudge work of killing bosses like Flame Leviathan. However, there's something disappointing about having him dead within the first week, so a middle-ground approach would perhaps have worked better; Ulduar would also benefit from a clearer progression path so guilds and ranking sites didn't have endless discussions over whether a hard mode is worth more than a kill a week earlier.
As to other penalties, well: if we start seeing raid-time cut-offs, enforced breaks and the like, WoW turns into a completely different kind of game. Server instability doesn't really help, of course; it enforces a break, but also extends and prolongs the raiding period, as guilds stay online longer to raid when the server's reliable. Even with fully reliable servers, though, the most health-aware hardcore raider will balk at what are effectively parental controls.
Even if encounters are hard, some guilds will still wipe on them. The real question is whether changing them after they've been defeated was a good move, as guilds still wiped on - and beat - the improved versions. Plus, whether having everything available at once was wise, causing confusion with progression paths, people trying to game ranking sites, and general bad feeling among guilds who couldn't aim for every single world first at once.
Bring back Molten Core, eh?
Disclaimer: I'm a member of a guild achieving several world first hard mode kills which were later trivialised, although I was away for the kills themselves and have observed this issue as a third party.