http://developer.gnome.org/projects/gup/proposals/dialog.html
"rationale: The eyes of people who read left-to-right tend towards the
upper-left and lower-right corners of boxes. Therefore the action the
user is most likely to perform should be located in the lower-right
corner. With this button order, the action the user is most likely to
perform is always in the same place and is always the most noticeable."
I've seen the comment. I've yet to see a single cite to the research
that backs this up. Slavish quoting from MacOS doesn't count.