The brilliance of Siri isn't the voice interface or the replies using text-to-speech -- it's just the name. People feel they are talking to another person, not a phone or a computer or a google. People understand Siri approximates a person, so they can interact with it informally and somewhat personally. You see it in all the news coverage. People refer to Siri as a person. It gets into your brain. Have you seen norm…
It's also a bit silly seeing people talking to "Siri" in public.