I never claimed it was perfect, but it does understand context. The key here though, is that it's in Beta. It's ability to understand context and natural input will be improved over time, and more services will be added allowing us to access more information.It's interesting that you would say that, seeing as a large quantity of responses Siri gives are indeed, "I don't understand."
I would challenge that.
For example, say to Siri: "What's the weather like in Paris?", and then after it answers, say: "What about in London?". That's a simple example, but it clearly shows my point. We'll only see improvements upon this, as well as the ability to access more information.