Adding support for other database management systems would require that the database logic be coded to the least common denominator. We have decided that we want to eventually allow add-ons in different languages, and thus the database becomes the only point where we can enforce accounting logic consistantly across all parts of the application. Porting and maintaining such logic across database systems is not feasible for this project.

Additionally PostgreSQL is an outstanding RDBMS and we have no desire to move from it.