Actually, Postgres doesn't require that you name the primary key
either - this is standard SQL92.
In order to double-check, I just tried the following:
create table foo (i integer primary key);
create table bar (j integer references foo);
The problem is that PG and SQL92 require you to define the *type* of
the column, i.e. integer. Grabbing this from the referenced primary
key is an Oracle extension. I happen to like it because the foreign
key reference is further walled-off from the primary key definition,
but it is non-standard ...
