I don't understand your argument. A new platform has to offer something the existing platforms don't have. Web apps cannot be the differentiator for a new phone OS because the big two already have standards-compliant web browsers. The browser is table stakes; of course any new phone OS must offer one, because you can't be taken seriously without it, but the browser in itself is not a reason to use the platform.

Or are you suggesting that new phone OSes ought to add proprietary non-standard browser extensions in place of a native apps API? Given the ugly history of proprietary browser features it is difficult to imagine anyone taking such a strategy seriously.