While people endlessly debate the relative importance of skill vs. gear, in the end it is obvious that you need both. Some people will always die at Heigan, no matter what gear they have. And nobody runs Naxxramas naked. The harder an encounter is, the more you need of both skill and gear. But when a challenge is easier, you need less. And as to some extent you can substitute one for the other, for the easier challenges you can choose whether to do them with little gear and lots of skill, or with lots of gear and little skill.
Where I am a bit disappointed with in Wrath of the Lich King is that people chose the lots of gear and little skill option for running heroics in so many cases. Certainly all PuGs do, which is maybe understandable, as you can verify a person's gear before you start, but have to assume he isn't very skilled. But that PuG approach ends up teaching players the general way to do heroics, and then even guild groups are run using PuG strategies: No crowd control at all, gather all mobs using AoE tanking, and then kill them with AoE spells. Blizzard even had to boost some classes AoE (e.g. Rogues) to make them playable in that environment.
When was the last time you saw a crowd control spell like polymorph sheep used? Contrary to popular belief Blizzard didn't remove those spells from the game. And I'm certain that heroics could be run with groups in much less good gear if we started to play better again, using crowd control like we did in the Burning Crusade. AoEing heroics down works, but needs better gear, and that somehow removes the purpose of running heroics in the first place. Everyone is expected to have gear better than the blues that drop, so most of them end up getting disenchanted, and the whole heroic loot is reduced to the one epic dropping from the final boss. And the fights aren't much fun, because the AoE strategy is dumb and repetitive. Another fine example of Raph's "players optimizing the fun out of games".