>>>I think it is free for non-commercial use only. IBM does the same thing with their DB2 database. Last time I checked, MySQL had the same language in their license agreement, but that was several months ago.
>>
>>MySQL has been GPL'd now (just so everyone knows).
>
>Cool. Now how do these guys make their money?

Academics, and the love of the game.

History of postgreSQL is at http://www.postgresql.org/docs/devhistory.html. The first postgreSQL was actually Ingres, created at Berkeley.

Large portions of UNIX and its tools were/are written this way.