The app installation app you describe is basically: an app store!
Functionally, the service lets us: find something, pay for it (unless it’s free), get it. So, Apple has done a lot to make all three of those dimensions work together: findability, ease of payment, ease of “installation.”
I think Apple is weakest at that global “find something” kind of findability–it isn’t that easy to find apps or content via iTunes. In contrast, for example, Google and Amazon have a lot going for them in helping people find things across big webs of choices.
Ease of payment is key: Apple gets people to have an account with an associated credit card, and then certain interactions via iTunes trigger charges, without us having to re-enter credit card info or establish a new account.
Amazon, Google and PayPal each provide similar services across the web, with Amazon’s tie-in to its own store being the most like iTunes.
A big part of the future for the Apple App store is in-app purchases like buying books. And that seems like a good example of how it’s the platform rather than the app format itself that’s enabling people to pay for things.
“Installation,” in terms of being HTML, is interesting–not so much because of any fine line between remote and local apps, but because of the idea of a collection of things (apps) that Apple has introduced with the iPhone.
It’s really findability again: having a set of things installed is about having a simple way to browse and organize “your things” more than it’s about having something be truly local vs remote (e.g., many iPhone apps don’t work at all without a remote connection–they are “installed” but almost like bookmarks to something online).