Really, really, really good engineers with keyword-compliant resumes walk in the door on Wall Street at 175k. I'm having a hard time with your numbers.
Cash compensation, yes. Total compensation -- I am arguing otherwise. SV engineers are asked to take more risk, and perhaps to sacrifice quality of life more. Thus higher expected compensation. That $175k in NY is probably $200k after bonus, so it makes sense that SV would be more.
Another way to look at it is that new grad is now close to $100k. The experienced guy is easily 10 times more productive. But only gets 1.5 in salary. So, he also gets 5-10 times as much equity, and that's valued because historically it made good money.