> But if every app is a web page, and all the code is out in
  > the open, it is quite easy for the user to disable and
  > strip out rent extraction code.

No. There should be more than a billion smartphones/tablets sold, what do you think is the ratio of those who can do what you told to those who have no idea? And what is the ratio of those who can willing to do it instead of just using the app?

And there is also the issue that if your app is just the web page, it is either universal and thus crap on all devices, or highly customized for each platform at which point it would be easier and less messy just to write it natively.