For the record, the comic is not derived from any personal feelings on the subject. I avoid playing the "Waaah, X Class is overpowered/Learn2Play, nub" wheel-of-fortune.
While I'm certainly under no impression that every class is perfectly balanced with every other class across every situation, I do subscribe to the notion that if you are unable to adequately fulfill your class' role, the problem is more likely to lie in the skill/gear department, as opposed to the "the developer's girlfriend must play X class, that's why it's better than my class" line of reasoning.
It occurs to me that that may just be an elaborate way of saying "Learn2Play", but while balancing is an ongoing process, I have seen any and every class in WoW played both poorly (looking at you, Fail-Druid) and fantastically. I think a lot of people need to come to terms with the strengths and limitations of their class choices.
If you're complaining because your Warlock can't tank 25-man Ulduar, it's entirely possible that the problem doesn't lie with Blizzard's "inability to balance classes".