A significant portion of my purchase decision was that OmniFocus was releasing a portable version of their program.
The trouble with browser-based iPhone apps -- around here, anyway -- is that you can't use them on the subway. The GMail client on my old blackberry was like that and it was totally worthless during most of the time I was mobile.
I do think that web apps with the HTML 5 database ( http://www.w3.org/html/wg/html5/#sql ) and clever caching would cover most use-cases. It does still leave email-outbox style functionality out of apps, but a simple message-passing service in the API would solve that.
I disagree about people wanting native installable apps. I don't think they particularly do any more.
I'd be really surprised if anyone bought the iPhone because of a certain app in the app store.