A good Engineer earning $140k as a base salary in SF shouldn't be a surprise (if it is, you're quite out of touch with the market) and then you have to add in the other costs companies have to budget for (benefits, stock, expenses, etc) plus it's clearly an average over the employees (so will include some that make much more and some that make less).

Honestly if it's surprise/shock it's _still_ a bit strange.