That's not true, both Firefox OS and Tizen use many not-yet-standard APIs. Luckily they are collaborating on many of these APIs and they will be interoperable.
The more you abstract, the more functionality you lose and the more generic your mobile apps will look. Facebook learned this lesson the hard way when they tried to make their mobile App in HTML5.
CSS, javascript, and DOM are just kudge piled upon kludge. HTML5 trying to shoehorn poorly thought out technologies created for hyperlinked static text documents into dynamic applications.
Until some disruptive technology completely replaces that massive HTML5 spec you speak of, the natives apps will always rule the mobile space and performance critical spaces.