I was thinking about this idea after the thread calmed down. I don't think PerlMonks has any intrinsic success factor other than Perl itself. I like what tye just said about it. I think there is another dimension to it as well. It's not only that discussing Perl is interesting it's that Perl attracts interesting personalities which makes agglutination natural.
On a Perl list, I once made a rather strange inside joke on a completely obscure 40 year-old pop-culture reference from another country. Two well-known Perl hackers got the reference and even extended it. I was struck by how bizarre but entirely Perl-ish the exchange was. I wondered if the same exchange would even be possible, let alone likely, on a list for any other language.