I personally have only anecdotal evidence, but I've read now many stories where the interviewers of these giants refuse to engage in a two-way, human-to-human conversation with the candidate but instead make the ordeal deliberately prolonged, stressful and unconfortable. I'd call that abuse.

Even though I'm sure there is a lot of variance between interviewers, I can't help but think that the abusive style of whiteboard grilling must "work" in that it results in able workforce, and that might be because of the reason I suggested.