..but most of it
Just because websites have hitherto been left in the hands of web developers and not app developers does not mean HTMLx and advanced js tools such as socket.io are not suitable for a web-app on a mobile device equipped with a decent browser.
A not insignificant percentage of apps are useless without a net connection anyway, so what's the difference? The twitter site for mobile would only need a few more tweaks (and it's not the available technology holding them back) for it to be every bit as good as an app.
The android browser already lays out bookmarks in a simple touch to launch way, and using a few tags in the HTML can turn a web-app into a bloody good imitation of a native app on the iPhone. I for one welcome the wide range of new HTML/CSS/js tools, although they do almost herald the death of the traditional web developer.