What can be done with no calculator or weather app on iPad?
Apple simply haven't made iPad apps for Weather or Calculator. This is intentional and nothing you have done. Apps with similar functionality are numerous on the App Store.

Additionally, the notification center does pull a local forecast, and many extensions can add exactly the weather information you prefer rather than just using Yahoo weather like the iPhone does. There are many regions in the world where local weather apps are superior to the ones on iPhone.