It isn't secret in the least; it's mentioned on their blog: http://blog.whatsapp.com/2011/09/?lang=en and at least one conference has had a presentation about it.
The idea is to help readers get an idea of which material is fresh and which material is more historical. Some dead material had to be removed.
The link is broken. Correspondence with the author (Robert Virding, 2014-06-17) suggested that the name is now mainly used as a conference presentation about historical aspects of Erlang. The interesting part in the original link was the section on the IO system and on process groups, Jobs and JCL. This isn't really covered anywhere else as far as I know. As at this commit, the original document is still to be found here: http://vidiowiki.com/media/paper/0m-V9dOL0AeY%20The_Erlang_Rationale.pdf
The 'download' link to CEAN has not been updated since R15B (2011!)
See mail on erlang-questions from Andreas Schumacher 2014-12-07
Daniel Freedman at Technion tipped me off about that.
Schlund was acquired a few years ago; unclear if they still use Erlang Textendo have a placeholder webpage and mail to Jeroen Koops (my contact there) bounces.
The .dtd and .ent files used to generate the FAQ (and Erlang documentation) were moved somewhere between R14B03 and R15B03. If xsltproc can't find them, it silently generates broken output. One symptom of breakage is that names like Björn get turned into Bjrn. This patch adds a check to make sure the .dtd and .ent files are there.