> I have a suspicion that a big part of why top-comp software companies keep their interviews so incredibly unpleasant has more to do with discouraging job-hopping among them (so, suppressing wages) than with its being the best process for hiring good developers.

You have to wonder if this has backfired. ;) Plenty of people job-hop every 1-2 years, and it's pretty common knowledge which companies ask which level of LC difficulty for which level.