If it was so overpowered, complain some, why did it take so long to nerf it? Ghostcrawler answers in this post.
It's not that they don't notice that something is overpowered, he says, but it does take some time to find a proper fix. Sometimes, it just isn't overpowered until a certain gear level. Sometimes, there may be bug fixes or larger problems that need answering first.Sometimes, they may need to debate over the proper way to fix it. Finally, they may have a more ambitious long-term solution in mind, and may have finally decided they can't delay until that's done.
You can actually sort of see that last one in play on the Hunter Ammo changes in 3.1, where they planned a complete overhaul of the system including phasing out consumable ammo altogether, but instead had to settle for removing the need for quivers and increasing stack size.
Another argument is that they're eliminating unqiueness and min-max potential. To that, Ghostcrawler responds, minmaxers do exist and can exist, but their playstyle should be defined by finding slight differences and little tweaks they can do to get their characters to the next level. When there's a big red arrow pointing at a specific thing, that means something's off and overpowered, and furthermore, takes away from the legitimate challenge of the whole thing.
These insights aren't necessarily new to many MMO veterans, but all the same, they're probably more or less true. It does, in fact, "suck to be nerfed" as Ghostcrawler puts it, but sometimes this type of thing is needful for the health of the game and even for the viability of the min-max playstyle in the long term. It's also interesting to note that he says that if you think something's off, we probably think so too, we just haven't had a chance to deal with it yet. Depending on which way you turn, that could be one more way of saying that they don't give in to the whiners, they just happen to see the same problems they see every once in a while.