"Caveat emptor" applies heavily in b2b transactions be they financial or otherwise. If you're buying a product then you need to spend money to hire sophisticated buyers, because if your buyers are dumber than the sales-people you're buying from they're going to be fleeced.
This is true if your buying a financial asset, a car or an enterprise software licence.
Just because Oracle sells into companies that could just as well have used postgres that doesn't mean that Oracle aren't producing anything of value, it just means they're taking advantage of the buyer being less sophisticated than they are.