I can't find the post where it was mentioned that the NY Times Style Guide is older than the AP Style Guide so I'm creating a new thread. First, I found this in an article about the NYT Style Guide which explains why you have a style guide:
Style guides dictate the aspects of writing not bound by the rules of grammar.
That's really what a style guide is for (consistency).
Now as to the NY Times Style Guide being older, it says:
As you also know, the Daily Journal and most daily newspapers follow Associated Press style. The New York Times does not. It follows its own style, most notably with the use of courtesy titles.
And from a Purdue University site:
Associated Press style provides guidelines for news writing. Many newspapers, magazines and public relations offices across the United States use AP style. Although some publications such as the New York Times have developed their own style guidelines, a basic knowledge of AP style is considered essential to those who want to work in print journalism.
So you're right. I said journalists follow the AP Style Guide. It seems the NY Times is the exception. But my statement is true, with the exception of a few like the NY Times.