PostgreSQL? I'm sure there are Oracle installations that would be difficult or impossible to replicate on PostgreSQL. But I'm also sure that the vast majority of databases would work fine under PostgreSQL. A "new project" in particular is unlikely to need anything that makes Oracle "special."
I agree the majority of cases where Oracle is used in small business segment is pretty good fit for PostgreSQL, especially considering the fact many of consulting shops who specialize in Oracle are willing to provide commercial support for PostgreSQL as well.
So what exactly would they choose instead for the role of high-quality relational DBMS (if DB2 for z/OS is not an option)?