Why does Siri always need the Internet?!

It's very frustrating and makes me not want to use the function. In a car or moving around I often experience network blackouts in the Countryside or underground on the tube.

Why doesn't Apple introduce off-line functionality for simple Siri tasks such as calculations, calendar entries, reminders and searches of data contained in the phone?

For me the most frustrating thing about Siri is asking a question and watching it spend half a minute working out a solution.