I'll try to put this as non-confrontationally as possible, since I think you're a level-headed, well-reasoned guy who has written a fine article, and I never like getting into flame wars, despite how overly-simplistic and dismissive I might be about to sound...
But I really think it is just about the hair.
Don't get me wrong, there are a few, like ChaserTech, who have very good reasons not to like the upcoming game. They want fluid Capcom fighting game combo engines to create really nifty videos demonstrating high levels of execution, creativity, and finesse. That's cool, the new game just isn't for them. But for the people who still complain about the changes to his appearance, and even those who claim that it isn't about appearance anymore (usually before they go into a rant about trivial BS, resolved issues and even outright falsehoods), I think the hair has never stopped being a problem for them, even if they don't know it.
Simply put, they want the game to be bad, and will seek out any information they can find to support that claim while rationalizing ways to dismiss any evidence to the contrary. This is due to my fairweather friend "confirmation bias," which outlines the human tendency to do exactly that. It's a sort of mental gymnastics, used to force the way we see the world to make it look the way we want it to. Sometimes it preserves our sanity, other times it turns us into incorrigible dickholes. Combine this with the entrenchment they've undergone defending their position against "traitors" who have opened up a little to see that the game has some good points, even if they're still not interested, and they gain a vested interest in defacing the game at every opportunity, exaggerating every small change into a franchise-ruining flaw (your mileage may vary on whether an issue is minor or major, I only mean people who overreact to everything). If they did not, they would be forced to change their worldview to accommodate the world, instead of the other way around. I don't mean to come off as snooty or elitist when I say things like this, because everyone has confirmation bias. I do it, too, though I try to recognize when I am and work against it. It's part of being human.
When someone says that all the haters care about is the hair, it's a bit of an generalization, yes, because it's aggravating when you're dismissed as an irrational "hater" simply because you have no interest in DmC and would prefer something more like DMC3 and 4. But when someone says that it isn't about the hair, then prattles on about how Dante is a "bad character" or the style ranking is "broken" or how the game is "Heavenly Sword with a jump button" or other depleted rhetoric, they can't admit that the reason they've constructed this elaborate fantasy, where every major journalist is wrong and that DmC is secretly a 2/10 game, is something as trivial as a hair style.
