Even though people know the primary action is the rightmost button, they can't help but stop on other elements because of that top-down left-right scanning that's ingrained in most people of the world. There's simply no better position that the very top left corner!
Another important distinction here is that I should not receive surprise dialog boxes as often as I currently do! Yet sooooo many apps throw unnecessary dialog boxes at you! Your step 2 "make decision" has happened before the dialog box appeared. It happened when I pressed the delete button on that file.
Whether step 2 is actually step 0 or not doesn't really matter. It has the same impact on both scenarios.
People only read strictly top down left to right (or right to left) if all other things are equal.
I don't know about you, but I've never been able to predict where the top left corner of the dialog will be to start reading. My eye is always instantly drawn to the big blue button that describes what will happen when I press it :)
Another important distinction here is that I should not receive surprise dialog boxes as often as I currently do! Yet sooooo many apps throw unnecessary dialog boxes at you! Your step 2 "make decision" has happened before the dialog box appeared. It happened when I pressed the delete button on that file.