It says where the data comes from: Glassdoor. Every time someone uses glassdoor to make claims about salaries in the Bay Area, someone else chimes in to say that they're way lower than their own experience. I wonder if there are two strata of software engineers operating there; a "chump" majority who are on the sort of salaries advertised, and a minority who are much more selective or self-confident and who post a lot on hacker news.