I never understood this, even while in the medical industry myself. Perhaps this might be a little true for an immigrant from Venezuela with a medical degree. But for an immigrant from England, Why not?
I'm talking about, for instance: being an orthopedic surgeon in England (or even France, or Russia). I operate on human bodies. Those human bodies work the same way in the United States, do they not?
Maybe there are some discrepancies in established best practices, country to country. But there is no necessity to go through the entirety of relearning fundamental medical knowledge just to demonstrate you didn't go to a "worse" medical school. Even if you did - what should be looked at is your medical practice, not school, and your patient track record.