Earlier quoted context omitted.
You had me with you until you used the phrase "foreign workers." It's not their foreignness that makes them cheaper, it's that (in the U.S. at least) they're not able to easily change jobs and demand fair market wages, because their visa ties them to one employer.
The foreignness makes them cheaper in that it makes it easier for companies to justify paying them less and forcing their loyalty through the visa regulations. It has nothing to do with their qualifications which are often excellent.
Such people get easily used up in these scenarios.