Thank you for taking the time to respond for precisely the reason you mentioned in your opening paragraph.
The one-liner would be included in the Change Log. I have a highly relevant example from the Runescape Game Client that happened today! Language selection was broken for the Mac version of the client. Users were unable to choose German/French/Portuguese worlds because of this.
A short fix was added to remedy this problem. But 99% of the users will never know this problem was fixed because Jagex doesn't maintain a public facing change log. Only a short "New:" for the most recent change.
Many Mac users who want to use the client but were prevented by being unable to change their language will never know once the next client update happens and the "New: Fixed Mac language selection" is removed. The fix was only mentioned by a Jagex employee on an infrequently browsed forum, where one day even the post will be lost once it goes past Page 50 (nothing is archived).
This is a scenario where a maintained Change Log (and public awareness of updates) would be highly beneficial to users.
The practice of tests has not caught on for all software - and more complex software often lacks pass/fail test builds for the public (eg: where are the tests for Photoshop?)
For apps - not everyone has unlimited data plans. So many people turn off automated updates. Data limits still exist at home for many non-U.S. users, so downloading updates on WiFi also isn't an option. Frequent updates (especially frequent, large updates) are annoying and prevent users from using an app due to data limits.
Due to said data limits, many people will only update when an update brings something beneficial. A useful feature, vastly improved performance, or important security fixes. Otherwise why waste the data?
>yet a tiny extremely-vocal set of people occasionally complain about changelogs if you make the mistake of writing software they install.
Change logs help developers too. Especially for open source projects [0] but also for internal projects. I'd argue it is less useful when the project is maintained entirely by a single person, as they will be aware of all changes they have made. However the moment there are 2 or more people working on the project, a change log becomes a useful asset for squashing bugs and keeping everyone up-to-date on important changes and deprecation changes of larger projects.
[0] http://keepachangelog.com/