So does Google, I am pretty sure it remembers your previous searches and knows therefore that if you are searching for "Paris" you mean the city and not "Paris Hilton" (or vice versa).
Kind of like how I just typed "When is thanksgiving day?" and Google told me the date. It understood my question and gave me the answer. How does Siri differ?
Try "will it rain tomorrow", or "should I wear a coat tomorrow"? Siri is an answer engine that tries to determine the meaning of your query and answer it. Google in recent years has started to add those capabilities to it's search interface, but it is not there yet.
Siri is much more like Wolfram Alpha or IBM's Watson then a standard search engine.
Bullshit - Siri has some special loops for recognizing questions about date, location and the weather. That's it. It really is not more advanced than "call xyz", except it not only uses the address book, but also the calendar and the weather service.
... Siri is a front-end to Wolfram Alpha and other data providers. It roughly identifies what you're looking for and forwards it along to the best data provider. Google has the advantage of being one of those data providers.