Triggers

Hello, I have this doubt since I started using PostgreSQL, a few months ago.

Why triggers are defined that way? I mean, in others DBMS you simply write:

CREATE TRIGGER <trigger_name> ... bla bla bla
BEGIN
  ....
END;

Why you should write a function first and then the trigger, which must call that function?

What are the advantages/disadvantages of that? Where can I find more information?

--
Germán Hüttemann Arza