My first thought when I read the tweet was something like: "Oh god, more dogmatic ignorance." In its immediate wake came the sorry realisation that this simplistic falsity would be mindlessly and endlessly retweeted by cheerful "grammar lovers" the world over. And the silly cycle is duly sustained.

Absolutely true, every word. Certain copy editors' obsession with the stylebook and its usually arbitrary rulings gives all copy editors a bad name.

Anecdote for you. When Web browsers were first being developed in the 90s, the folks who implemented them added a convenience feature whereby you could specify a color using either a code (like "#00ff00") or a name (like "green"). Most browsers would accept either "grey" or "gray" -- except Internet Explorer, which stubbornly recognized only "gray", and simply ignored any reference to "grey". (This has been fixed in recent versions of the browser.)

Is the problem really the person who posts on the APStylebook Twitter feed? I would interpret this tweet, and any tweet coming from that feed, as having an implied "According to AP Style," in front of it. It seems like the problem is the people "who imagine that AP publishes a rule book rather than a stylebook", as you say.

Gray is more common in American English. . . .
And as always, one wonders how much of its frequency in American English is attributable to American copy editors changing grey to gray because their style guides tell them to.

"Gray" is in Noah Webster's original 1828 dictionary; so is "grey", but all it says is "see GRAY". So I think we can take it that "gray" has been the standard AmE spelling long before the AP stylebook, or indeed the AP, were in existence.

A copy editor busily changing "grey" to "gray" is harming no one and has less time for mischief. (It will be a miracle if I've read correctly the two words I'm supposed to type in.)

Next thing you'll be telling me is that there is no Santa Claus. As I am forced to edit according to British style, this is helpful. I can't tell you how galling it is for me everytime I have to add the S to the end of "toward."

If someone is making a list of priorities for editors, changing grey to gray should be near the bottom. It is inefficient and misguided, particularly at copy desks with fewer and fewer editors.

Maybe AP needs some critics to annually select the top ten most useful entries in the stylebook (I vote for the one that helps me sort out how to refer to the sizes of various guns), and the bottom 25 least useful entries. Prune regularly.

@John Cowan -- Noah Webster's dictionary is not a reliable guide to common spellings of the time. He managed to change colour to color and gaol to jail, but he didn't get enough supporters to spell ache as ake. It seems equally possible he changed gray to grey because he thought it needed to be changed. He may have made changes that people now regard as useful, but he was a man of many peeves.

And of course the "grey" in "greyhound" has nothing to do with color. The etymology is a matter of much discussion, but color ain't in the running.