Are you sure you're using the same definitions as the author? In practice, across a pretty decent sample of large tech companies, I've never seen a truly structured interview outside of Matasano, where I was almost murdered by my employees for instituting them. I think we'd hear far more complaints about them if they were common.

It's possible that what you consider to be a structured interview is in fact what this author (and I) would call unstructured. Specifically: if the interviewer has any discretion about questions at all, the interview is probably fundamentally unstructured.

In a structured interview, the interview is less an interrogator than a proctor or a referee. Every candidate gets identical questions. The questions themselves are structured to generate answers that facilitate apples-apples comparisons between candidates: they generate lists of facts. The most common interview questions, those of the form "how would you solve this problem", are themselves not well suited to these kinds of interviews. It takes a lot of work to distill a structured interview out of those kinds of problems.