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There's no such requirement. At one point, they required everything to be in native Objective-C code or HTML/JS (both were allowed) but they have lifted even that restriction.

No kidding - that's great to hear.

Off hand, browsing the source, it looks like a web app (index.html, CSS, JS). "With offline support" makes more sense in that context too, as you would expect a native iOS app to be mostly 'offline' anyway (sans perhaps streaming video).

I think this means it's a website designed for iOS and using the new HTML5 offline storage stuff for local operation.

That would be more up John Resig's alley as well.

That's pretty cool!

Yep - we recently built a mobile app that utilizes local storage for offline support, with sync functionality for when users are connected again. HTML5 really opens the door for some awesome stuff.

Note that you combine the two approaches. In a native app you can embed a webkit window and show HTML/Javascript. Since the Khan exercises are written in Javascript this could be the plan (but I don't know).

Yep, anyone wanting to do this: PhoneGap.