That is precisely the case. In fact, if you go to the effort of using the browser on your iOS device, Apple considers that an "alternative means of purchasing

That is precisely the case. In fact, if you go to the effort of using the browser on your iOS device, Apple considers that an "alternative means of purchasing." Indeed, if you past a link to the webapp onto your springboard, and launch it from there, Apple _still_ considers that an alternative means of purchasing. You really have to be purchasing through an native application before apple asks for a cut.