The article was originally written in 1996, and describes GNU policy. As a cultural artifact, it's been incredibly effective but is now outmoded, as what it describes is very solidly the norm, as you note. So today it serves as a statement of GNU policy and as a historical artifact, and isn't so much something that is relevant to today's readers.

Since the article specifically calls out Perl:

In the Perl 4 days (1991 until whenever Perl 5 (1994) gained critical mass), the O'Reilly book Programming Perl was the Perl documentation. Besides the book, the only other official documentation was the perl(1) man page, which (while lengthy at nearly 30,000 words) was not nearly as complete as the O'Reilly book.