It is true, you can make really awesome apps with HTML5/CSS. We, ourselves, are doing the same thing.
We are bringing to attention some new concepts that we think have not been taken into acount into HTML simply because HTML features have just been stacked together and it HTML simply evolved into something it was not intended to.
On the other hand, the HTML5 completion date has been announced as 2020. Do you really think HTML5 will still suit the needs of the web then? It should probably be HTML7.