[danaris]

The assumption they're claiming lunarhustler made is that engineers in Silicon Valley and engineers in (say) Utica, NY work at approximately the same speed and quality.

The assumption dorwi's asking you to make is that moving to Silicon Valley somehow makes you work twice as fast, or that only engineers who work twice as fast live there.

Basically, lunarhustler is making the assumption that humans who can program end up at roughly the same quality no matter where they live or how much you pay them, while dorwi is making the assumption that how much you are paid is directly related to your productive output.