This is completely in line with the premise above. If the database is primarily a data store, unseen by the end user, then Postgress, Firebird etc are fine. I

This is completely in line with the premise above. If the database is primarily a data store, unseen by the end user, then Postgress, Firebird etc are fine. If however the database is an active part of the development stack, being used by lots of "users", writing new code etc, then commercial offerings with better tooling win.