Originally Posted by
TenDance
You know why? Because Blizzard handed out wellfare epics later in the game. Everyone who wanted some gear got his PvP-weapons, no skill needed, only grind. The same goes for the shiny epics you got for tokens. Doing your daily heroic had been enough to get you some nice pieces of gear, after they implemented the 128-ilvl-gear most people simply overgeared Karazhan. Add in some gear you got from some of the factions and that the crafted gear had been really good (honestly, every second priest got the crafted set, feral"tanks" could bear with that 'till BT) and yes, Karazhan had been puggable. Especially with those players in mind which already got a lot of T4-loot, sometimes even T5 and still pugged to farm some tokens.
Try Karazhan in green and blue gear, with at best some parts of D3, and you will meet some sweet enragetimers. Bosses like the curator had been the classic example of a content blocker. You had to meet certain criteria to pass, or, in short: gear.