I don't mean to overreact, but so were <object> and <embed>, which were what Flash used. If they're creating their own canvas-based way of rendering a UI, it's not really using HTML5... it's just that HTML5 happens to be the container.

And just because it's open source, doesn't mean it's standards-based.

I'll have to dig deeper, but things like "HTML and CSS independent" feel very proprietary to me. It just feels like you're losing out on the shared semantic value of HTML, etc.