Siri has lots of known problems. My biggest gripes are the lack of context and lack of a "discussion" state.
But Siri is a general domain problem, which is really really hard. Siri set the expectation you can ask it anything, and it works terribly and for most questions just gives up and runs a web search.
If you are an e-commerce company though, that's a narrow enough domain, because you know that for most people, they're looking for products to buy or compare. It's not an unbounded Q&A service.
