That's why I said "essentially". :) Compared to the alternative where salaries are location independent, it functions as a change in salary.
> Given folks can live where they like
Switching costs for moving are relatively low for young, healthy, childless renters, but are much higher for many others. Not wanting to move away from family (who may also be providing free childcare for you), not wanting to move away from close friends (who studies repeatedly show are critical for mental health), not wanting to disrupt your child's or partner's education, needing to find a buyer for your old house, finding a new house to buy, being underwater on your loan, not wanting to change doctors while in the middle of a long-term or chronic illness, having a hobby or passion that is highly location dependent, etc.
Moving is hard. Anyone who thinks it isn't likely hasn't put down roots enough to realize the benefits that accrue from not moving.