Even many "native" apps just embed the native browser as a widget. Development is often much faster that way and they can fall back to native APIs for those few features HTML5 doesn't give them access too
I'm not sure that's true. I think there are some fairly popular mobile apps using a webview. The facebook app? Honestly I don't know if that's true but their mobile website has almost the exact same UX. There's a few subtle differences but maybe those come from some glue around a webview and not all brand new code.
Either Native -> HTML5 with things like Mandreel (http://www.mandreel.com/)
or
HTML5 to Native with things like cocoon.js (http://ludei.com/tech/cocoonjs)
Even many "native" apps just embed the native browser as a widget. Development is often much faster that way and they can fall back to native APIs for those few features HTML5 doesn't give them access too