^ This is as good of speculation as anything. According to the link you provided, the AS amounts to something that someone demanded of you. Why not? If someone wants to sell something on Craigslist, or anywhere else, they need to write a for sale ad, and I don’t see the AS as being a whole lot different, except that it’s typically much more of an indirect or even oblique way of writing: “Buy my stuff so I don’t have to get a real job!”
Perhaps more pertinently, the development of the university system of education through the early 20th century was a big deal in the US. While I don’t remember when schools of art and architecture became part of the U system, I do recall several of my art history profs saying that the university system of education essentially replaced the artist’s guild system, which was the previous standard for an art education.
In doing a little bone head research over a few days courtesy of Mr. Google, I’ve found a near absence of references to any formal study of the history of the AS. I poked through Google scholar and a bunch of other references. As far as this kind of dork research goes, there is no direct account i came across that even hints at a direct answer to the question of origins. If I were still a student it would be fun to take a Michel Foucault like approach to the development of the AS.
Perhaps the history of the AS is not all that important to the question of using one, but to pursue this, the next logical step would be to contact an art history prof at one of the local U’s to see if she/he has any knowledge on the topic. I don’t plan to do this but someone with an interest might fire off an email. During my studies of art history we talked about a lot of stuff, but i don't recall the topic of an AS coming up. That was back in the 80s. As the article you linked clearly shows, it’s now part of the curricula.