If you think about it, the way we chat/message on chatting/messaging applications [Yahoo Messenger, Google Talk, Facebook Messenger, Google Wave, etc.] is broadly similar to how we use a command-line interface. We type something, and a response comes from the other side. This other side could be a human or a machine, but that doesn't change the fundamental nature of the interface. We could fix a meeting or a short vacation with a friend over a chat program, and likewise we should be able to order a pizza using a chatbot. Not much different.
Update [Jun'16]: If you think about it, the way we use Web search engines, it's also similar to using a command prompt. You enter some text [which acts like a command], and it returns some results. Similarly, the !Bang feature on DuckDuckGo is like entering commands on a command line, complete with a specific syntax to be followed.