I absolutely agree that the main aim of an interview is to determine if a candidate is able to think in a structured and analytical way. I'm much more interested in talking about situations when you might choose UDP over TCP, rather than being able to recite the details of a particular HTTP specification
Besides, you can dig deeper in any direction, depending on the candidate profile. For a network engineer, understanding on the packet level is important. For a web programmer, the interaction between server and client is important (HTTP headers, MIME types etc, webserver scalability etc.). For a sysadmin, understanding of processes and interaction of applications and OS is important. All those can be derived just from a simple question -- what happens when you click on a link
besides, you can silently participate in the interview, or review the sound recording afterwards.