What an economic retard you are. What would the salaries be for "Systems" Ph.D. in Computer Science if all the foreigner were sent packing? Hmmm. Double probably.
If you are a natural US citizen, and your GREs are anywhere close to good, you will waltz into any good Ph.D. program in CS, because there are very few USC applicants who are willing to do the (incredibly intense, shitty, thankless) work required to attain that level of education. This isn't your typical IT administrator stuff...think more along the lines of the nexus of advanced mathematics, systems design, and operations research.
The nationality of admitted students at this level has very little to do with any profit motive either, as almost everything admitted to these types of Ph.D. programs are fully funded (by assistantships that require a ton of hard work, almost slave labor, but still funded). An international student will actually *cost* the university more than a USC, on average.
I am very close to people who sit on the admissions committee at my university...they certainly don't pass over USCs for their health.