It's not just UIs. I was in the closed beta for a computer game (friend was a dev), and one of the goals of the developers was to lower the barriers to entry for new players to get into the genre. Nearly universally, the self-described 'hardcore' players decried the changes as dumbing down the game and removing the skill barriers between new and old players. In fact, some of those changes were UI upgrades, like making the item shop easier to navigate. While that one was more generally accepted, there was still a vocal minority that thought that noobs being able to easily purchase the items they had earned would lower the competitive aspect of the game.

While there's often an initial loud and forceful resistance to change, it dies down as people get used to the new system, except for a few die-hards. In the example above, it took about two months for the community to come around and realize that removing some obvious pain points let the players focus more on strategy and whatnot. Of course, it helps that the new system is clearly superior to the old system. Microsoft Office's Ribbon, on the other hand, is not clearly superior, so people still bitch about it years after it was introduced. I happen to think it's superior in theory, but the implementation was botched a bit (menu names and organization not intuitive), so it's not a clear upgrade.