I'm not sure this is obvious. 1) Apple is a multi-national company, and hires an employee in the UK. 2) This employee relocates to the US
At what point do they displace the US citizen? All Apple jobs are not earmarked for US citizens (+residents, etc...), and they're already doing the job when they move to the US. Unless they're hired abroad for the express purpose of relocating to the US, then it's not "obvious" to me that they've displaced anyone.
Suppose I work in an org with dev teams in multiple countries. If I relocate from one site to another, am I freeing up a slot in the country I leave and taking one in the country I move to?