Hi! I am the author of this post. I think that taking the user to `www.foobar.com` when he/she typed `foobar` does violate the expectations for most users. All browsers which I've used take the user to their selected search engine. Most people outside of HN do not know that what they type in that search bar would be visible to anyone listening on the wire.
It's funny how this expectation had changed over time. In early browsers like Mosaic and Netscape, the expectation was that you'd enter a domain name or full URL and there would be a DNS query. When newer browsers incorporated search into the address bar, many of us considered this to be leaking information to search providers. For quite a while I disabled that feature.