It's actually originating from a real source, and denying that by attributing it to grognardism and agendas won't get at the real reason for it.
This isn't an unreasoned attack on 4e by blind, ignorant barbarians who thunder and roar when exposed to fire like some sort of cartoonish Frankenstein's Monster. "NNNG! 4E BAAAAD!"
No, this is a problem noted by a lot of very clever and very astute individuals, repeated time and time again. This is something more than unreasoned hatred.
And for what it's worth, I can see how 2e trufans leveled that criticism against 3e, and how much more they can level that same criticism at 4e. This isn't a new problem, it's just a worse problem.
The "real" source isn't what you think it is. It's the same source that happened at the release of each and every other edition. You could stat up the "haters" as a PC class, they would have maintained more consistency through the editions than the actual classes in the PHBs.
I never called anyone blind or ignorant. Some people just react badly to change, even clever and astute individuals. A relatively normal person, when faced with change, simply decides if that change works for them or not, makes their choice, and moves on. A more deranged individual (and I mean that with love) believes that the whole world must feel the depth of their rage about the change, especially those who have embraced the change.
It remains, though, that the D&D game has always been a game focused on combat. It's always been a game of killing things and taking their stuff. Fighting and treasure have always been the core values of the game. The other stuff is largely group dependent. Some groups RP very heavily, some not at all, most in between. Some spend hours on character background (despite never having a set of rules for backgrounds, gee, what a concept), some write "parents killed by orcs" and move on. Some groups love dungeon crawls, some love urban settings, some love the wide wilderness, some love plane hopping, but all those elements lead to the combats and the treasure. All those great classic modules from OD&D, 1e? Mostly combat. As ALWAYS the level of RP and backstory and other elements are DM and group dependent, not rules dependent. Extra subsystems create more rules clash, problems for groups that don't enjoy those prescribed play elements, as cutting them out can have some reprecussions in other areas. It's easier to add things than take them away.