It looks like neocities uses subdomains to host user sites.[1] They probably don't want to pollute the subdomain "space" with their own content. They probably have some kind of automatic rewrite thing going on as well.

Now I'm wondering how you do the auto-subdomain thing. Maybe have *.neocities.org A record to the same IP and then have the HTTP server parse the URL?

[1] from the blog: http://mlpfim.neocities.org/