If an iPhone app is developed in JavaScript not in Objective-C can it be accepted ?
Advantage being not technical but marketing since the app store is much more exposed to traffic. For example app store is linked from homepage: http://www.apple.com/iphone/
No. Apple maintains a Web Apps catalog for web apps rather than displaying them on the App Store. They have a separate submission form to get your app in the catalog.
Since the user doesn't download and install a web app in the same way they download a native iPhone app, it wouldn't quite make sense to include it in the App Store. The user can still put your web app on their home screen by using Add Bookmark in Safari.