Is this for real? I can name numerous advantages of Web Apps have over desktop/native Apps, "Building better interfaces" is not one of them.
Trying to build a UI with CSS and DOM manipulation (not to mention <div> hacks, Bootstrap, Dojo/JQueryUI, different rendering engines, etc) is an exercise in pain compared to basically _any_ modern UI toolkit. (From XAML to Qt, Android, hell even GTK.)
edit: minor correction, I meant to say " build a UI" not "build a native UI"