The reality is that there are lots of native iPhone apps that should be web apps. Right now, the web apps don't quite pay as well.
I believe what we're ultimately seeing is the rise of the native/web hybrid application. These are a class of web-like applications that can run in disconnected mode:
* views use HTML/CSS stored locally on the client
* handling of requests from the views is done within the client itself, or dispatched externally to a web API
* sophisticated data structures can be persisted on the client (in mysql, text files, etc.)
* more sophisticated processing than typically occurs in your standard web app
* better access to native hardware features
The technologies are coming together: Adobe AIR, UIWebView/iPhone SDK, Android's WebView, etc. to support this. I'm looking forward to it.