Here's an example of how one company apparently applies that "no American available" policy:
Now I am working in an American multinational here in the United States, and I find that every last person working for me is an H1B temp work visa holder. There are zero Americans on my staff. In addition to that, we recently had to fill 3 more headcount in my group. My boss instructed me that due to 'budget' that we were to go to our India sourcing department and they would arrange for contractors to be sent in from offshore (India). It would take about 1 month for their visas to be arranged and for them to be on site (in Raleigh North Carolina). Though our Applicant tracking system is overflowing with applications by Americans (including probably some of my own old ones), we didn't even look at those before bringing in the H1Bs. The corporate law firm arranges this, gives the 'no Americans can be found' stamp of approval and the temps are flown in with expedited Visas (H1B or other temp type visas that they use until the H1B is approved). I mentioned this to a couple of my coworkers, and I was discretely told to be quiet about it if I knew what was good for me and didn't want to 'expire' myself.