It seems to me that from the university's standpoint, a company is considered a plus instead of corruption, i.e. have "real-world" impact, and perhaps the university will have a stake in the company as well (not sure about this). If so, it is a win-win situation for both the university management and the professor, only the student lose, and who cares about that little grad student?

Typically not a stake that I know of but a school like MIT makes a lot of money from technology licensing.

Is this where “tech transfer” comes in and the University gets a piece of the departing business or a perpetual licensing agreement?

Universities often benefit from it financially. There almost always is an agreement between the professor and the university.

Everyone makes money?