Seems strange indeed, I took a quick glance and since this url loads fine:
I think this url should work too:
But it's strange that url gives a 404?
I see the sources for both urls on your gh-pages branch.
Since both of those files exist in gh-pages branch, it definitely seems like both should be available via the urls above? But seems the second is not working. So maybe it's a gh-pages bug?
I found on stackoverflow, it looks like some other people have had trouble with some gh-pages showing 404 errors, so maybe it's a github pages issue?: http://stackoverflow.com/questions/11577147/how-to-fix-page-404-on-github-page
Also (separate from your gh-pages issue), I think hoplon libraries are in flux at the moment (documentation and new versions are in process of being updated to the hoplon github repo). But I saw the demos here are up to date with latest and greatest: https://github.com/hoplon/demos. So you might want to start fresh by basing your experiments off of one of the demos there. If you use the new stuff, you might have better success doing a prod deploy (I think the latest version will fail gracefully if phantomjs isn't installed).