A few years ago, I applied to a senior Windows dev position. As I recall, they needed someone primarily to port existing software. One of the first interview questions was about how I would optimize shell sort for some particular edge case. The interviewer did not appear to have any papers with her that contained shell sort. I don't know if she thought I would remember it (last time I implemented it was high school), or what.
In months of sporadic interviewing, I don't recall being asked a single question relevant to Windows development, engineering strategies, how I comment my checkins, or any of a million other things which seem much more vital to me. Every interview centered on puzzles and algorithms. Every job listing was for Windows/C++ with various platform-specific technology requirements that I fit.
Personally, I think a lot of employers just like to have perpetual job openings. It makes the company look good. Also, I think that a very, very large percentage of the "screening" is really just to provide justification to the subconscious decision that was made within moments. There's a reason that Silicon Valley is almost entirely white, male, and under 40, and it has nothing to do with technical aptitude.