The fact is that the living costs (largest chunk being accommodation) varies so drastically, that it feels hard to justify having the same salary and basing salary purely on skill, with the assumption that location truly is a choice and people have chosen to live somewhere cheaper. We have people who end up paying $2,500/mo rent and others where it is more like $800/mo or even less.
In addition, we always want to pay people more if they choose to move somewhere more expensive, it seems unfair if someone gets used to a salary in one place and suddenly they move somewhere much more expensive, and we don't help them out.
I'd love any more thoughts you have on this :)