The GitHub page is currently a much better introduction to Incanter than the web page.
Also most HNers are familiar with GitHub and since Incanter makes good use of its features, it would be hard to make incanter.org a better resource for people just getting started.
They use GitHub to the max so I'm guessing they actually like GitHub. I've heard people who like GitHub complain about other code hosting sites not having a source tree on the project website. Never heard an avid GitHubber complain about the source tree on the project website. So I'm guessing that it suits their aesthetic just fine.
Also most HNers are familiar with GitHub and since Incanter makes good use of its features, it would be hard to make incanter.org a better resource for people just getting started.