90 or 100 seems small in comparison to the number of tech workers in SF making that kind of cash
For government you have to factor in job security, generous pension and benefits, and guaranteed annual pay raises.
Engineers have none of those things.
How about employees making $200K or over? That's 1790, or just about 4%. $100K or over? 15997 employees, or around 39%. So over 60% of SF city employees make under $100K. The median salary, in fact, is just under $86K.
I could be wrong, but I suspect that's lower than Facebook's median salary.