- $150,000 is much less than a top-flight engineer like the one you're describing might make; it's not out of the realm of possibility for what an engineer with a good pedigree might make his first year out of school, if he went to work for a big company.
- The engineer went to school for four/five/six years and then went to work. The doctor who earns $300-400k went through a four-year university degree, four years of medical school, and a residency or fellowship before he started earning money. Some specialists, like neurosurgeons, take at least 11 years after getting their undergraduate degree before they really "get their wings." Not only are their then-substantial salaries offset by the huge delay in getting those salaries (residents make, what, $35k?) but they also have to pay for things like malpractice insurance, which can be in the six-figure range.