There's been a big back-and-forth about how big an impact QA can make on information-retrieval. A few points:
Writing a proper natural language question isn't necessarily easier than writing a Google query. You don't always know what you need to know, and providing feedback from the QA system is very difficult. You can iterate towards the right query fairly well, as your searching teaches you better keywords.
The percentage of queries that can be answered by a single sentence is substantial, but might be smaller than you think. People also use search engines to navigate around, to find long articles of interest, and to carry out tasks (e.g. shopping).
The strictly informational queries probably aren't that important to Google's revenue. The best queries to be serving are the ones where the user wants to buy something, because that's where people will pay for advertising. If a competitor takes away the informational searches but can't serve the commerce searches too, I doubt Google will be sweating much.
True. When I said that, I was thinking of a service that does what Watson does and gives Google-style answers.
So, if the query "What is the capital of the United States" was made, at the top it would say Washington D.C. and after that it would show search results, similar to how Google shows answers to unit conversion searches.
http://blog.reddit.com/2011/02/ibm-watson-research-team-answers-your.html