> (ie, work sample tests), I do not understand why any tech company does developer hiring in any other way.Because every method of hiring has its own biases and tradeoffs. Requiring work samples biases against programmers who aren't interested in doing a "homework assignment". For example, I don't enjoy whiteboard interviews but I'd rather write some fragments in front of the interviewer and "think out loud" instead of working on a multi-hour (or multi-day) coding project. Writing on a whiteboard is just not that big of a pressure cooker to me.
One could argue that the majority would prefer self-paced work samples instead of whiteboard interviews and you're optimizing for a wider candidate pool. That's fine but it's still a tradeoff. I think you're running a smaller scale boutique firm so work samples makes sense for you.
For a company like Google Inc who is more selective[1] than Harvard University, I don't see a compelling need for them to rely on work samples. That company is so desirable for programmers that any "work samples" Google tries to standardize on would get leaked and endlessly discussed on stackoverflow (see FizzBuzz for precedence.) If Google has to keep changing out the work samples to stay ahead of the street knowledge, you've lost the ability to compare work samples over the years which was one of the motivations to use that method in the first place.
At their scale and selectivity, the "study your algorithms book and prepare to be grilled on the whiteboard" seems to work best for them. Yes, they reject a lot of false-negatives but it's offset by ... their scale and selectivity. They can afford to reject false-negatives. If their screening methods were truly terrible, I don't see how the label "ex-Googler" would have the currency it does in the marketplace.
[1]http://thenextweb.com/google/2010/09/14/one-half-of-one-perc...