Doctors, nurses and lawyers often have to think quickly, on the spot, in life or death (or at least life-altering) situations.

A developer (in a non-pathological work environment) has time to discuss and research a solution.

FWIW I don't remember the last time I had to implement a binary tree since my C++ course in college; I'm not a fan of pop quizzes in interviews, but if you're going to do them then at least make it relevant to the work you do on a daily basis.