It doesn't fail at UX - it's intended to be a presentation manually controlled by the presenter. Just because someone posted a link to Hacker News doesn't mean the author intended for it to be here.
Even if I had seen a message beforehand telling me "just use the arrows to navigate", I still wouldn't have found those arrows. Light gray on light green doesn't exactly stand out.
I put all my presentations on the web because Linux + projectors = sadness, and I often end up having to borrow someone else's laptop to give the talk.