It isn't an app in the Apple app store so the title is misleading. It is an online web service that you browse to. Apple wouldn't ban that anyway.
That said, in the case of a Bitcoin wallet, Coinpunk is unique because it's implementation is primarily in client-side Javascript. Most of the wallet services either rely on server-side crypto, or native apps.
Because of that technological dependency, either the service controls your data, or the mobile app store controls the distribution of the app.
With Coinpunk, no one can control it. No one. It's yours and always will be.