Well, it depends. If Atwood's aiming at an international audience, then he should use both measurement systems. If he's happy with an American audience then there's no reason for him to bother.
I note that the date of his blog post is the international-friendly “November 19, 2012” rather than the American numeric “11/19/2012”. But internationalising dates like this is easier than providing measurements in dual units.
Indeed. MM/DD/YY is used informally and for datapoints (e.g. the Date field when you sign a form), but any time you are writing formally (e.g. a letter) you use Month DD, YYYY.
It's almost like MM/DD/YY is the abbreviation of "Month DD, YYYY"
