I guess I'll answer from a different perspective: When I hired folks that knocked it out of the park on those kinds of technical interviews, I didn't ever have a problem with those employees from a technical skills perspective (other types of issues, like work ethic or interpersonal skills, sure). On the other hand, when I had folks who were borderline iffy on those types of questions, but we hired anyway due to success in other interviews, I came to regret that hiring decision fairly often (definitely not all the time, and some of the folks in this bucket were stellar, but certainly noticeably more technical aptitude problems on average).