But unlike in his "Next" example, "OK" does not imply any progressive series of dialog boxes. It just confirms an action.
That derails his train of thought completely.
As an aside, there's most probably nothing inherent in progressing from left to right, it's just an artifact of Western scripts.
Why do Hebrews or Arabs also play the same piano? To be in touch with the rest of the piano-playing world, they just got used to it.
And that's the main argument for "OK left": Since most UIs have used that order for a long, long time, it is (arguably) "right".
At least I'm very disturbed every time a UI amateur imposes his pet order "Cancel/OK" on me.
And brake and accelerate pedals in the car? Also has nothing to do with "progress on the right".
Simple explanation:
You do the major tasks with your stronger foot, which is for most people the right foot. The left is only occasionally used when changing gear.
The right foot sits comfortably on the right side, so that's where accelerate is, because you're using that most. Brake is only used intermittently, so it is located in the second-most convenient place for the right foot.