I'm not sure if it is a 100% perfect analogy to real-world economics, but the best analogy is that all money you use in Starcraft is "working capital". Money in the bank only does you any good insofar as it allows you to handle unexpected emergencies, all other cash should be deployed towards your goals. Which in Starcraft would be to defeat your opponent with generating more cash as a subordinate objective, and in business would be to either make as much money as possible throughout the history of your company, or fulfill whichever goals your company has. Amazon does this by keeping low margins to discourage competition and reinvesting as much as possible.

The biggest difference between Starcraft economics and real-world economics is that Starcraft has no regular expenses or debt, so there is no way to go bankrupt. This removes a large risk element in reinvesting your money.