If you go to one of the referenced sites: http://www.vegasworld.com. It asks you to enable flash first then will fall back to the html5 site. I wonder why that fallback is configured.
Doesn't sound that mysterious to me. By the sounds of it, Flash is still their main platform (for performance reasons perhaps), and HTML5 is provided for those who don't have Flash installed. Haxe can target both Flash and HTML5, so this doesn't contradict the article.