All places I've worked that have multiple locations adjust salary both up and down when employees move to different markets. It's all about the prevailing rate for labor where you are located, and not some measurement of the "value you provide".

Yes, but I assume these are all markets where these companies have physical presence. I doubt many are adjusting up because you want to move to London because you like the fog.

Sure, but 'remote' is the 'location', not home town.

You don't pay a non-London salary because the employee lives outside, or a Euro-denominated one because they commute from Paris.