It occurs to me that if someone came out with a new technology and said "hey, you can now describe your entire interface's structure in one markup language, the visual look in a second language, and the code in a third language, and then your app will run anywhere that has the required runtime interpreter" they'd be shouted down faster than you can say "go Swing".

Yet that's essentially what HTML5 apps are all about -describing the interface in markup and processing it at runtime. In what way is native not always going to be better for a given platform?