Do Americans leave the ordinal suffix out of dates? By 'ordinal suffix' I mean '-th', '-nd', '-rd', e.g. 'April 17' instead of 'April 17th'. If they do, is there an explanation for this behavior?
However, since the ordinal is nearly always pronounced when the date is read, I think this seems absurd. Searching around the internet has not revealed any reason to leave out the ordinal beside an appeal to these authorities. I have no idea why they think this is good style.
I write out the ordinals, and would encourage others to do so as well, style guides not withstanding.
America's a big place, and you're likely to find people that speak and write it differently. I'm an American and I've been known to write both "December 31" and "December 31st", or "31st of December", though usually "12/31" suffices. When I speak, I virtually always say the suffix... something like "December the thirty-first." I wouldn't be confused or surprised by seeing it any of these ways.
I mean, you might as well ask why French people eat parsnips. I assume some have and do, some haven't and don't, some aren't even aware of choices they've made in that regard and at the end of the day it doesn't really matter or characterize the French people in any meaningful way (do all non-American people always add the ordinal suffix? If no, why not, and why should the answer for Americans be any different?).
I would assume it's because you're writing a number, which doesn't require letters, unless of course you're spelling it out, as would be the case as the first word of a sentence. Why tag on letters to something when it can be easily typed as a simple number?
I've done journalistic transcription, and even if the person speaking says, for example, "April 15th" we're required to type it as "April 15". Even though, in your head, your pronounce it as "April 15th" when you read it. However, when the speaker says, for example, "The 15th of April" it is typed out as just that.