A blast from the past: from a 2009 posting on writing dates:
… any number of manuals tell you that you must not write {January 13th} (curly brackets enclose written material); only {January 13} is acceptable. The usual defense is that {January 13th} is prolix, because it has an unncessary {th}. Omit Needless Letters, or something like that.
What makes this proscription especially bizarre is that {January 13} must be read as “January thirteenth”. I cannot say “I met him on January thirteen”. That is, {January 13th} is faithful (but, to some people’s measures, not well-formed).
So there’s an orthography-to-pronunciation convention. Ok, I guess. But what riles me is all those advice sites that dump on {January 13th} and the like, as if they were signs of idiocy. Why do people care so much?
Some publications have taken the matter in hand and decided to spell such dates rationally. The Economist, in particular, is consistent in its spellings. A recent issue uses the rational spelling in its headers:
The Economist September 10th, 2011
and in the text, as in this example from “The Libyan dilemma” on p. 45 on that issue:
On September 6th, China issued a white paper on its “peaceful development” (ie, rise) …
I’ve started using this variant myself.