I think that generally, yes, people lie/embellish/exaggerate, especially about things like their salary and especially on the Internet. I cannot speak to any situation in the SF bay area, but I have caught people telling this lie, and had people confess to telling this lie.
I fail to see what someone would gain from doing so. A few lies? Sure... But so many?
But mostly I'd just say that people like to have something impressive and interesting to say, and making up numbers is a quick way to do that.