Well, the strategy i'm describing involves a native app. In that case, would it be possible to expose device-specific API to JavaScript?
Also, multi-touch is actually supported by webkit. There a nice WWDC video that intoduces this capability if you'd like to learn more.
To be clear the idea above isn't new of course. For instance http://www.appcelerator.com/ provides a native app with a thin wrapper around a web control.