Google's profit is a few hundred thousand per employee per year. Let's call that an anchor for how much room there is to give in salary.
I was contacted by Google last summer for a potential job. I was shocked at how mediocre their recruiting staff were - unfocused, intentionally vague/evasive, rambling, didn't answer my questions, didn't followup when they said they would. Perhaps Google can't convince some people to uproot their lives and move across country because they're not doing a very convincing job in their initial outreach?