A little story.
My buddy from college told me this a few days ago actually. His bosses best friend had been unemployed for the past years. He has been looking diligently for the past 2 years for a job (he has a ton of experience a masters) and has not found much at all.
My buddies boss decides to give him a temporary position in the company and boom, two months later he scores a big interview with a company (who he had applied to a month earlier through a temp agency and he was told they were not interested in hm). A week after that, he has a job and a damn good one at that.
When I was unemployed, the first piece of advice I was given by a temp agency was to get a job anywhere I could get hired. She told me that many of their clients refuse to even look at resumes of people who are not currently employed (regardless of what the current employment is). She said that this was one of the easiest ways for most of these companys to shift through the thousands of applications they are receiving for jobs.
While I do not agree with the practice in general, when receiving literally thousands of applications for a single job, you have to do something to separate out the resumes, and I guess this method is working for them.