There are plenty of companies that just dont want to use open source stuff.
Whether its a valid reason or not, they just feel that it cant be that good as it is free.
On a side note, im not implying postgresql is better or worse than Oracle. To be frank, i wouldnt be able to say why one would be better/worse than the other as im pretty much a noobie when it comes to db's.
But i do know, when you have plans to start a business and you need a backend db, postgres is much more appealing from financial point of view.