Once big difference is that they require a certain amount of manpower, so they can't afford to throw away good material due to an inaccurate screening process. I guess in contrast Google can (probably?) afford to be wasteful.
"One of the interesting things we've found, when trying to predict how well somebody we've hired is going to perform when we evaluate them a year or two later, is one of the best indicators of success within the company was getting the worst possible score on one of your interviews. We rank people from one to four, and if you got a one on one of your interviews, that was a really good indicator of success."
http://gawker.com/5392947/googles-broken-hiring-process (The first quote)
Possibly nothing is worse for a new tech venture than a bad hire. I've lived through a few at various startups. It's horrible. It's the worst kind of death because its often slow and painful and you're bleeding capital.
Also realize that a bad/incompetent programmer is a NET NEGATIVE.... not just net 0!
(obviously being 'ridiculous' is subjective, and highly dependent on the roles and responsibilities of the job).
Google on the other hand actually could afford to be less ridiculous.. they just choose not to.
I've thought A LOT about this problem... so much so that my web-startup is attempting to solve one aspect of this problem (see my HN profile for the link).