Based on products like Siri or Cortana it may seem like we are coming closer to NLU, but the reason those are working at all is because they are very topic-specific and tiny subproblems of what NLU is really about.
One of the great things about the semantic web, to me, was always that you could process it on a cheap VPS or your own desktop, creating new systems with little or no knowledge of math or machine learning. (I know projects that do this today.) That's not going to happen for a long time with natural language processing.
Why do you think this? Is it just a feel or is there some company that is really close. As another user mentioned in this thread natural language understanding seems to be the same thing as solving strong AI. Solving strong AI is a huge deal. So big that the people in control of it will probably become the most powerful people in the world.
I doubt that a sufficiently well-defined notion of natural language understanding that does not specifically include strong artificial intelligence in its definition would require strong AI. Constructing such a definition is left as an exercise to the reader.
Thinking that strong AI is required for natural language understanding may end up being similar to how it was once thought that beating humans at chess would require advanced AI. Brute forse can do wonderful things, as can weak AI.
I'd love to find out more about what you have in mind here. Can you elaborate?