You must exist on a different Internet and reality from me. :-)
Not that long ago, there was an article on HN about an internal hiring consultant (I think) telling someone that if you don't currently have a job, don't bother applying. I've heard project managers yammer on about how companies use layoffs to get rid of their least productive employees.
In a down economy, when HR is faced with a flood of resumes, they start looking for simple things which give the appearance of objectivity and wisdom, which arbitrarily reduce their pile of resumes. 'Currently employed' becomes one of these criteria.
If you're referencing the same article(s) I've read recently, it wasn't "if you don't currently have a job, don't bother applying" it was "if someone has been unemployed for over a year, there is probably a reason". It wasn't a negative judgment on being laid off, it was making the assumption that a long period of unemployment was a signal that the person may not be very hard working or talented or whatever, and with many candidates to choose from that signal could be a deciding factor.