The article does rather skip over that and starts by assuming that regardless of ordering you're aligning your buttons to the right of the dialog.

You could go with OK/Cancel and left align the buttons so it's easier to find the OK button.

Windows seems to go with OK/Cancel right aligned, which would be a little odd given the point you made.

I guess the use of whitespace to visually group the buttons makes it easy enough to find the button group and from there you read them left to right.

Would definitely be a interesting study to see the relative effects of aligning things to borders and visual grouping through use of whitespace.