"Does this person not realize that wikipedia is also run on a web server."

The difference is that you don't have to run your own server to edit or otherwise participate in Wikipedia. You don't need your own server to have a blog on Tumblr or WordPress.com.

And since Simplest Federated Wiki requires either Ruby/Sinatra or Node.js/Express, you need more than just a shared hosting account to run it, which raises the barrier to entry (though the one-click installer, or PaaS providers, help lower it again).

It may eventually be a non-issue if someone builds a "wordpress.com for federated wikis."