The Warlock community was in an uproar over the extremely quick hotfix that Blizzard applied to nerf Conflagrate among other niggling issues with the recent Patch 3.1. Aside from the fact that nerfs are never a fun thing, Warlock players pointed out that Death Knights, while acknowledged by Blizzard to be overpowered, reigned for months before getting nerfed (somewhat) in the latest patch. Warlocks also pointed an accusatory finger at Holy Paladins, who dominated Arenas throughout Season 5 and promptly got a fix along with Death Knights.
On the other hand. it took all of 24 hours for Warlocks to enjoy insane Conflagrate numbers, which was promptly fixed. Ghostcrawler explain why through a lengthy response over at the forums, noting that Death Knights were imbalanced for more reasons than a simply overpowered spell coefficient. He also said that Death Knights and Paladins were nerfed over the course of several patches leading to Patch 3.1, but none proved to be enough to balance them.
It needs to be said that Death Knights were changed the most in this patch, with talent trees completely revised, some notable abilities removed (oh, Shadow of Death, how we'll miss you...), and class mechanics changed. It's quite possible that even these changes won't curb Death Knight dominance, but it's a massive change that simply isn't hotfixable. It's a fair response and a pretty good read. Ghostcrawler makes several important points, one of which is that players shouldn't feel that developers don't love them. So don't be emo.