You’re absolutely correct though, the parent comment seems to think there are absolute right and wrong answers for UI. I think that’s just not true, a good UI is one that works for your customers.
Of course there are absolute right and wrong answers for UI. Accessibility, minimum text contrast and font size, minimum size for clickable items. Keyboard shortcuts may not be (or may be) one of them, but in fact consistency across applications _is_ considered a hallmark of good UI and every Human Interface Guideline I've ever read, including open source ones such as that from KDE, specify such.
You're being obtuse. Even most of those you list will not reasonably have a fixed, absolute value that is right for all users, all applications, and all situations, and assuming they do is the cause of a lot of awful UI limitations.
(Your user will never need characters to render as single pixels? Try again - sooner or later someone will decide to abuse your spreadsheet as a raytracer and be annoyed they can't make cells single pixel)
And a feeling of consistentency often requires exceptions for specific cases such as the example of "find" where few users want to specifically find what happens to be in the browsers idea of what the document currently contains, but what it logically contains in their model of what it should contain. Consistency means that in an app that dynamically updates a scrollable region, for example, it should still find things in the currently not part of the browser document bits, and so shouldn't use the browsers find in those cases.
Some users might want a shortcut that always does the browsers own find, and there generally ought to be ways to override the app, but consistently acting how the user will want is rarely compatible with absolute rules.
I agree with almost all of the specific examples you give, but I think I agree _because_ those UI decisions work better for customers, and not because they are absolute right and wrong. I think I can illustrate this with some examples:
1. Consider a keyboard without an f-key, eg Arabic. If the user is using an Arabic keyboard, what should bring up the browsers 'find' functionality. Of course ctrl-f won't cut it. Perhaps it should be ctrl-[first letter of 'find' in Arabic]? Or perhaps ctrl-[the letter in the same position as f on qwerty keyboard]? It makes sense to follow convention if one is already established for Arabic, but then what about languages that are new to the web?
2. Consider a phone-tree, which is a sort of UI. For this UI, the 'absolute right answers' of minimum text contrast, font size, keyboard shortcuts, etc, make no sense, but there are surely other ways to make the UI work well for customers.
In both these scenarios, I feel the 'right' choice is to pick the UI that is best for users. I think there isn't a-priori a right answer, and users habits change over time and across cultures, so it's not necessarily an easy choice.
