Oh yes really. I have had candidates with PhDs in computer science who had a deep understanding of static analysis of programming languages, but who did not kn

Oh yes really. I have had candidates with PhDs in computer science who had a deep understanding of static analysis of programming languages, but who did not know how many bytes were in a pointer on a 64 bit operating system, who thought that there was an algorithm for compressing any 64 bit number into a 32 bit number, who could not describe the possible consequences of a buffer overrun in C, and who had no idea whatsoever what a virtual function table was. Now, to be fair, as Dijkstra is said to have pointed out, astronomers are not experts on telescope building. People with deep knowledge in one small area of a field are often ignorant of other areas, even closely related areas. In those cases it's even more important to get a sense for how the candidate approaches problem solving, whether they can learn on the job, and so on, because you know that they are going to be deeply in problem solving mode very quickly when faced with their first real-world problems. I hold up myself as a case in point; I helped build the JavaScript engine that was in Internet Explorer in the 1990s, but know practically nothing about HTML, the browser DOM, CSS, and so on. If I were interviewing someone like me for a web developer position, I would have to be convinced that the candidate could learn quickly.