The typical iOS user has become accustomed to using native apps over the browser. It's very hard to battle habitual behavior. Additionally, every time iOS users are given a mobile web app, until VERY recently, those experiences have been miserable . . . . and seriously, if you're on iOS (especially iPhone, not so much iPad), you know what I mean.
Therefore, the routinized web app sucking and not feeling as "snappy" as a native has just put web-apps in a damn rut. I would absolutely LOVE for user to get into the habit of using WebApps, but unfortunately, Apple has a HUGE incentive to keep users funneled to native ones.