Thanks for clarifying. I'm a bit disappointed in Google about this. I would much prefer the apis to be shared completely between the 2 models and don't see why they can't be.
Also, installable web apps should be something not specific to Chrome. Why not make this an open standard so I can install my apps to other browsers without extra effort from the app developer.
As i said, the work is being done on APIs. Infact in developer channels of the browser, I think all the html5 APIs are accessible to everyone. As for background pages, there is no way of running a background page that is hosted somewhere else because there is an internal api that allows communication between pages's javascript in realtime. And such communication would not be possible with a hosted file.
And there is a thing known as installable web-apps. Which basically means you can install an app with just one manifest file hosted online. (it used to be in about:flags but now i think it has landed in stable release, but not sure). Which means no hassle of webstore or even maintaining a separate crx file, just upload a manifest.js once and forget :) Unfortunately background processing is not possible in hosted apps, just in installable ones.
Also, installable web apps should be something not specific to Chrome. Why not make this an open standard so I can install my apps to other browsers without extra effort from the app developer.