[bumby]

Besides the obvious point made by another commenter that two completely equivalent people won't exist, it's not just negotiating skill it's more about negotiating leverage.

A real example that I've seen: two workers work for the same employer and have been given offers from other companies located in a different State. The single mother in the group had significantly less leverage because she (and presumably her employer) knew she couldn't move without potentially affecting the custody of her kids. She didn't get a raise.

Or to extend your example, someone living in KC has less leverage because they cannot use the COL argument to justify higher pay. If I'm being courted by an employer to move, you better believe I'm building COL considerations into my overall salary ask.

[Dirlewanger]

Right, and employers are going to exploit these leverage imbalances in any way possible. It's why I don't think we'll ever see "equal work for equal pay" as seen in the article. You're just not going to get high COL wages while living in a low COL area.

[bumby]

Not to mention that the original intent of "equal work for equal pay" was about gender disparities. The importance being: gender (technically, 'sex') is a protected class, low-COL-resident is not.