It wouldn't surprise me if their bashing were correct, but I doubt that it's PostgreSQL's fault.
I download the db source (inside opencrx-1.9.1-core.postgresql-8.zip) and executed their three schema files, dbcreate-indexes.sql, dbcreate-views.sql, dbcreate-tables.sql. Each of the 118 tables has a three-field composite primary key of 'PRIMARY KEY (object_rid, object_oid, object_idx)'. object_rid and object_oid are both VARCHAR(200). There are *no* foreign key constraints. Each table has between 15 and 50 fields, with 25 looking about average.
Gee, why to table joins take so long? Maybe because a blind monkey created the schema? Normalized databases do tend to perform better, so I hear.