There is one part of the H1B program i have not seen mentioned which I think explains why the industry likes them so much. H1B workers are pretty tightly linked to their job and won't quit, because they would jeopardize their visa, and later their Green Card application process. I have seen a lot of H1Bs working for years maintaining crappy legacy code while they were waiting for their visa number. Americans on that team would ask to be transfered to another project or quit.

The other hidden face of that program is that a lot of H1B workers are employed by staffing companies who are taking advantage of them ruthlessly.