So it should use the HTML5 video if you have opted into YouTube's HTML5 trial. This will only be used for new articles, but I went ahead and re-published the article you linked.

The solution is HTML5 video, but that relatively young technology requires further development to meet the needs — and DRM requirements — of a service like Netflix. According to the blog post ...

Fullscreen APIs: The Fullscreen APIs in HTML5 mean YouTube can offer an immersive full-screen viewing experience with a standard HTML interface. Before this became available, a lot of extra code ...

However, HTML5 Reset has a very nifty class for clearing floats without extra markup, so I ended up incorporating that element into my own Sass-based boilerplate code.

The video-format war between HTML5 and Adobe Systems' Flash is old news. More than half of Web video is now compatible with HTML5.