Can you give some specific examples? In my experience (which I also verified to make sure), all of the things you mention act on keydown. The exceptions are on multi-key combinations, which follow a special key that is held down while modifiers are entered, where the action is completed by releasing this special key (ALT + TAB [...TAB | SHIFT]) being a common example.
TAB is otherwise immediate, as is ESC, and the examples of typing, as well. So I'm left wondering, how do they have it wrong?
> all of the things you mention act on keydown
Because they listed the exceptions to the "act on keyup" rule
If only one case follows your rule, and everything else ever implemented from the start of personal computers is an exception, your rule is awry.
The GP means that, if you hold space down on a button, you can then tab to another button without activating the first one.