Note: This article lists examples which take place within fandoms; not the TV Trope's opinion as to whether a change is for the worse. TV Trope doesn't have opinions. The focus is on over-reaction about minor changes.
This seems to be the mentality of quite a few people about when the webcomic Megatokyo underwent Cerebus Syndrome. The comic basically switched its fanbase from "people who know about shoujo manga" to "people who like shoujo manga and/or character-based plots", so while the quality is still good and the update problem has arguably improved, it did cut a few people out of its main circle. And since these people are those who don't like things...well...
Interestingly, the comic's Cerberus Syndrome was directly connected to one of the two primary creators leaving the comic. There had actually been several "what if" comics to the tune of "what if one of the two creators gained sole control?" The fact that some of the "joke" overdone plotlines in the what-ifs ended up actually being used in the comic once it became single-writer is Hilarious in Hindsight to even fans that didn't bail out after the change.
The character of Fanboy in the Magic: The Gathering webcomic UG Madness plays out this trope a lot, mimicking the fanbase of the game, as seen here. The actual author of the comic, though, is more reasonable, as show in strips such as this.
Homestuck gets this audience reaction with Act 5 and the Trolls, and later with Act 6 and the new humans. The author even Lampshades it:
"Since then, the author has been steadily updating PROBLEM SLEUTH 2, which you [Jane] have been following avidly. You are happy that he stayed in that lane, and stuck with a time-tested formula. If he went in a different direction, you probably would have found it really disappointing."
Parodied in Unwinder's Tall Comics where Unwinder didn't even like the original books in question, yet he still feels the need to criticize the upcoming film adaptation.
Unwinder: The guy who's directing it is Nathan Blaine. Director of Elite Force Vampire. Amy: Yeah, I remember that. ... Didn't you hate those books? Maybe it'll be an improvement!
Penny Arcade showed this as a rite of passage for Gabe's descent into Dungeons and Dragons fandom because he now had a version of the game to hate for not being the version he started with.
Parodied in San Antonio Rock City: one strip beings with a fan walking up to Mitch Clem demanding that he bring back Nothing Nice to Say to which he says "fine". This is followed by an exact copy of a previous SARC strip with the characters replaced by those of NNTS. The last panel shows the fan appreciating this strip and claiming on how much "better" it is.
xkcd parodies this with "Workflow". The change: the program no longer overheats your computer when you hold down the spacebar. The complaint: someone with a Complexity Addiction had configured their system to interpret a rapid temperature rise as a useful command.
A lot of fans of Sinfest screamed this when Tatsuya Ishida embraced radical second-wave feminism and changed the comic style from Black Comedy and subversive Take Thats at religion to a downright odd and thought provoking world where everything is controlled Matrix-Style by commercialism and male chauvinism. His attitude towards those people has not made things better.
Planet Zebeth isn't unknown for the occasional filler comics here and there, but thanks to the author running into some financial hardships for several years, he started to put in even more filler showing his Author Avatar ranting about the state of the economy and the filler rants seem to have taken over in terms of updates since there hasn't been any actual updates in the comics for a long time. Many fans have given up and no longer watch the site after getting very tired of the author's countless political rants that had taken over the site.