Can an iphone app developed using html5, CSS and Javascript be sold through Apple store ?
As long as there is no porn, free thinking, anti-apple content or anything else Apple see's as bad for them, I don't see why not
But why wouldn't you just make it a web app?
Yes, but you will still to use Xcode to compile it into a iOS binary. You might need an additional framework to do this. A example is Phonegap that turns HTML into a stand alone iPhone application. It also does cool stuff (when compiled into an iOS app) like enabling GPS and Tilt sensors.
Why not? Make an application that is just embedding the standard web browser.
Then point it to your application URL on the Internet (or even on the iPhone itself?).
I don't know if this any help but it's a list of all the web apps on apple's website. Not sure if this is linked to app store but they do list them!
You can develop almost all of an app using HTML5/CSS/Javascript. 99.9% etc.
However at least a tiny portion (from a short template or a library) needs to be in Objective C to initialize a UIWebView containing the HTML web app source files, and the app bundle will need to be built using Xcode for submission to the App store.
Apple may or may not require some additional functionality beyond that of a simple web app before accepting an app into the App store. (There have been anecdotal reports both ways.)