> 'apps' do not necessarily have this same requirement
But a great many do. Many of the 'apps' on Google's web store are literally just normal web apps doing their normal thing, expect that Google is presenting them as though they don't work in anything but Chrome.
> No server is needed in this scenario
Where is the html/etc hosted?
For example, I was working on a finance management app in Chrome along the lines of Quicken or MsMoney. The 'app' used plain HTML, jQuery and local storage to function and save your transactions. No server is needed in this scenario and I surely wouldn't call this a website or an extension.