I think you are creating false equivalencies. There is a huge difference between the risk and commitment that an entrepreneur brings to a venture when compared to any other employee.
Now, if an employee (engineer or not) participates with similar exposure they definitely deserve more than a salary.
Maybe you haven't had a solid failure yet. I have. I lost everything once. And by that I mean everything: home, cars, furniture, even the last penny in my bank account. Everything.
My employees got laid off and found new jobs. Their lives continued (something I was happy to see, BTW). For me it was a nightmare that lasted a few years until I was able to get back on my feet (through entrepreneurship, again).
Everything in business in business isn't rosy. Businesses like Facebook that go from dorm to rocketship with hardly any struggle are pink unicorns. Most ventures have to slog it out and struggle, sometimes for years, before they succeed (and most fail). In this context, paying market rates --which means "only as much as you have to"-- is the fiduciary responsibility of the entrepreneur/CEO. Over-paying because of some unconventional criteria of fairness (that happens to be false) is simply irresponsible.
Because of this and other experiences I am very sensitive to this idea that everyone is equal (in terms of salaries, responsibility, exposure, risk, etc.). That's not the case at all.