[illumin8]

Clearly, a talented engineer in the UK might be just as smart and experienced as a principal engineer at a big tech company in the US.

But, this doesn't have to make sense for it to be true. It's simple supply and demand economics. There is a greater demand for top-tier talent in the SF Bay Area because most of the technical leadership is there and they want their best engineers working closely with them. It's not hard to understand.

I read once that the single most significant indicator of where a large company will locate its headquarters is the CEO's home address. It doesn't take a rocket scientist to know that if the CEO lives in the bay area, so will his top leadership, and so will their top employees.