@danluu a hypothesis to your appendix B in https://danluu.com/bimodal-compensation/ …: 50% of the most profitable US companies per employee are software (source: http://www.businessinsider.com/apple-facebook-alphabet-most-profitable-companies-per-employee-2017-12 …). The more profit per employee, the higher salary per employee.
IMO this seems like evidence against, since the hardware companies on the list (Qualcomm, Cisco, TSMC, ARM before it was acquired by SoftBank) don't pay nearly as well as software companies that have never made money.