I think by the time you gone thru all the trouble to build HTML App that only works on certain device, you would already build a native app faster and easier. That's what happened to Facebook. The web app is not multiplatform, so, why even bother. And if it is multiplatform, you are limited to what web standards offers you. And if you have done web development, you know browsers don't play well to each other, FF and Chrome has different scroll width standard. So, packing an app with all sorts of multiplatform patches are just a big pain. Might as well do native app and isolate the quality assurance to its single platform.