What 3.x people disliked was that this new version of D&D was supplanting our preferred edition, and if we got on board with it because we wanted to "keep playing D&D" then it meant we had to adopt elements of play and game presuppositions that we didn't like or weren't interested in. So we had to decide whether we wanted to keep playing the brand labeled D&D or whether we wanted to keep playing the game system labeled 3.x or OGL. Many of us went with the second option.
And this is exactly where I find myself now with 5e on the horizon. There is little I can do to change WotC's direction on 5e as an individual, but at the same time, they can't break into my house and burn my books, nor can they uninstall my offline (and illegally updated) tools; I can keep playing 4e. If I don't like 5e, that's probably what I'll do, until I find something I like better. If someone finds a way to put out a 4e clone under the OGL, so much the better (it's being actively worked on).
But could we reverse this? If there were a game on the market that was in every way like 4e but was called something else, like "Murray Clook's Arcania Unoerthed" would many of the partisans of 4e given it a look? Some very well may have, but I suspect the vast majority would have stuck with the D&D brand. I suspect in part that's because, absent the D&D brand, it would have seemed too different from what they understood D&D to be.
I don't know. In 2007, I was very anti-WotC, and ready to bail on D&D entirely. I was actively looking for a new game; my group and I were tired of the warts, the system mastery, the imbalances at higher levels, the ridiculous prep time, the broken math, and on and on. I tried every D20 variant I could get my hands on, including E6 and the Pathfinder Alpha/Beta, Arcana Unearthed, the Books of Experimental Might, etc, and none of them fixed the issues or pushed the right buttons. I was, at the time, leaning toward using BRP, or several other runners-up to replace D&D at my gametable. The last thing I wanted any part of was 4e.
Then one of the guys in the group
made us try it. It took me a little while to come around and see the merits of the system, but eventually, it just "clicked." The rest is history. I'm not saying that my experience is universal, but I assure you that it is far from unique. I am well aware that not everyone would have made such a jump; some people play whatever the "current" flavour is, and some play just because it is called "D&D", and they have their reasons, I'm sure. That said, I'm willing to bet that many of the folks that bailed on 3.x for 4e because they were looking for something different still would have found 4e-by-a-different-name.
Here's an analogy, and honestly what many "arguments" I've heard sound like:
Nintendo has lost a lot of money recently (very few people have been buying the Wii recently). They also announced a new system recently to replace the one that wasn't selling.
But to call the Wii a flop would be ridiculous.
I've said this before, but I'll reiterate it again, there is such a thing as market saturation. 3.x reached it, 4e reached it very quickly (although DDI is still growing way faster than I would've expected), and Pathfinder will reach it as well (just much slower, apparently). And splat books won't keep this from happening, any more than new Wii games will keep Nintendo from moving on.
This is a pretty decent analogy, actually.