The Postgres-Driver for DBD (traditionally ?) has postgresql as dependency. But it libpq should be enough. This ends up in installing the whole postgresql suite instead of just the client library. Not quite optimal ;-P Seems, in 7.x times there was only one big monolithic postgesql port and the splittof was done later, which has not been reflected in dependencies.
*** This bug has been marked as a duplicate of 158950 ***
Dupe.