High finance (banking, PE, hedge funds) are basically the only career I know of where you begin at a relatively high salary, and have potentially unlimited career growth (in terms of salary and earning power), where at the highest end, you aren't doing substantially different work than you did at the beginning (this is simplistic, obviously. You work at a higher level, and begin to employ people to do the work you did previously. My point is that the career progression doesn't require a change to realize the highest earnings).
Am I wrong? To become a "millionaire" (using it as a synonym for wildly financially successful) doctor or lawyer, you generally make the majority of your money through either an invention or marketing skills. What career isn't a "dead end" applying this logic? Real estate, maybe?