Seems entirely possible that Silicon Valley doesn't host a disproportionate amount of sex scandals. Maybe there's something about the PR culture, or the relationship with news media such that sex scandals actually get reported on.
My guess, after working in old large corporations, is that the Silicon Valley people aren't quite as cozy with reporters and lawyers. They haven't had time to develop tactics for getting reporters to not report on juicy sex scandals. They haven't had time to come up with a play book for dealing with sex scandals.