That $140k number might be a reasonable 50th percentile for what a junior engineer would make at a startup in the Bay Area, but compensation can increase quite a bit after several years in the industry, especially for engineers who move to large companies which give stock compensation. They will far outpace the earnings growth of engineers elsewhere.
It's much easier to achieve that kind of career trajectory in places with high concentrations of tech companies, e.g. the Bay Area and Seattle.
Now I'm sure the BA people average better but somebody in the top 5% from St Louis is going to be pretty good.
Note: I'm from Auckland, New Zealand and $US 100k would be a very good salary.