[xxqs]

nope, this is all about understanding the logic and how the system components interact with each other.

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

[tomblomfield]

I agree - you can memorise answers on a fairly generic level, but digging deeper in a relevant area, or talking about edge cases, exposes whether a person really understands what's going on.

[xxqs]

besides, how can one memorize if the questions are unknown?