And it's not like GNU is unique in having other documentation beyond man pages. Most FLOSS projects these days use man as a simple summary of command-line argum

And it's not like GNU is unique in having other documentation beyond man pages. Most FLOSS projects these days use man as a simple summary of command-line arguments, and have the rest of their documentation in HTML. The BSD folks are the only ones that have stuck to their guns of using man as the primary source of documentation. GNU man pages also helpfully tell you that more documentation is available in info format, which something many other projects don't do.