Honestly, if you wrote Siri as a text line parser, would anyone be impressed by all the fancy features? It's more that current voice response systems are so incredibly primitive.
I think most people would be impressed if they could just type in what they wanted as an English sentence. Most users are familiar with GUIs, and may have heard of command line interfaces, but an English interface would be new. And maybe a plain English typed interface would even be useful. Some percentage of people type full English sentences into Google.