The app wasn't actually produced by Wikileaks, just by an enterprising developer who charged $1.99 (for stuff you can read free lots of places). It let you read the leaked documents and follow the Wikileaks Twitter feed. No reason has been given for its removal although Tech Crunch says the app does not appear to violate Apple's terms of service. Meanwhile, same app is up and running in the Android store. And that says a lot about both stores.