I know the reason for it! But the fact remains that it's two actions that are superficially the same (press an affirmative sort of key to trigger a highlighted

I know the reason for it! But the fact remains that it's two actions that are superficially the same (press an affirmative sort of key to trigger a highlighted button), and users who choose wrong lose data. That's... pretty much a one-sentence definition of bad UX :D The same system would make perfect sense if it only had one focus target. Dialog comes up, the "main" action is focused, tab cycles the focus, space/enter select it, and escape cancels the dialog. There'd be nothing to learn and nothing to remember.