Indeed. I really doubt Apple prefers foreigners in their hiring (it's a rather significant hassle to bring somebody in). If anything, citizens have some edge.
But once an immigrant has been hired, the PERM process essentially would require trying to hire for that position again, and employers (not just Apple) are anything but motivated to replace an experienced and qualified employee with several years' experience at the company with an untested new hire, so they treat this process as a Kabuki performance.