It's all really the same. All bosses before Ulduar were "hard" at some point. Sure, people just went in and cleared the content, cause we had a preemptive strategy to work off of. All of the kind hearted players who ran the Naxxramas content in the "Vanilla WoW", and even the lucky few who ran through during The Burning Crusade, all knew what they were up against, and all had an idea of what was going to happen in there. So, when the time came in Wrath of the Lich King, people knew exactly what to do in these fights and situations, which were toned down slightly and revamped for 10 and 25 players, rather than the classic 40.