Spot on, here's a cookie
Seriously people, vanilla WoW was NOT hard, not even Naxxramas. What it was, really, is a grind fest. Hours upon hours to farm specific gear, buffs, etc, on a personal level, and collecting enough players with <insert items> to form a raid.
Remember going back to Maraudon when AQ opened for nature res pieces? Now people already know, they'll be prepared before hitting 60.
Remember one of the most nightmarish fights, the Four Horsemen? The problem: having enough tanks that can't miss taunts.
Compare everything from vanilla to, say, heroic Kil'jaeden, and suddenly the old raids don't seem that scary anymore, do they?