Dollars spent per staff member is a metric that should necessarily increase over time as automation increases. Fewer and fewer staff is required for all of the costs.
At somewhere elite like Facebook many of those staff members are probably being paid about half of that in compensation. And then they have massive server farms to run.
I'm not equating that to how much each staff member costs, i'm saying thats what each staff member on average is roughly responsible for spending each year!
This is why I get confused when someone on HN says it would be easy and quick for a competitor to replace Facebook or Google. It's only easy if you can support such costs year over year over a decade or more.
The amount of software and hardware solutions that get developed over that time creates a great entry barrier. That's not to say that it's impossible for a competitor to appear with a great idea and execution and over time become the next big thing, but it's critical to emphasize that it's going to take a long time of large year over year investment to get there.