Hi Jeff,
I may not be making myself clear. The “context” I’m thinking of is almost every other desktop application I use. I can only speak for myself, but repeatedly using common software has trained me to expect UIs to work a certain way (the “user model”).
True, only in some software (e.g., MS Office, Eclipse, Adobe Reader X) is it necessary to press Enter to highlight the first result. In other software (Chrome, Firefox, Google Drive) pressing Enter is not necessary to highlight the first result; but it does jump to the next result. This isn’t at issue, but as you’ve quoted Bill Higgins against “violating users’ unwritten expectations of how a web application should look and behave” I can guess at what you might prefer.
The details of pressing Enter only confuse the point. All I was trying to say is that the unfamiliar Ctrl-F behaviour was a frustration after 10 minutes of browsing the Discourse demo, especially when it had unintended consequences like navigating to a completely different page.