The author is using Chrome. He could set up search engines to use in the Omnibar instead of visiting DuckDuckGo (e.g. ama[TAB] to perform a search directly on Amazon.com).
No, it wouldn't. You can just as easily perform searches on those other sites directly from Chrome's Omnibar without having to go through a middleman like DuckDuckGo.
http://support.google.com/chrome/bin/answer.py?hl=en&ans...