I agree that in the long run it would be better for users; yet as a user, I'm used to clicking on the Okay button on the left. Every time I see one isolated application with the Okay button on the right, I'm going to have a slower/harder time knowing which button I need to press.

If one of your users uses 50 applications, and he uses yours once in a week, he's going to be annoyed at your application for being different; even if that "different" is supposedly better, reflexes have taught the user to scan the buttons in a certain way.

I'm not suggesting that the order we have now is better; but until one of the OSs or an application like Facebook moves to the "better" button order, I can't see why a designer might do so for his own application.