Controlling Reuslts with Limit

Hi,
I was reading through Bruce's on line . I found follwing bit unclear...

"Notice that each query uses ORDER BY . Although this clause is not required,
LIMIT without ORDER BY returns random rows from the query, which would be
useless. "

When I run a query several time I get the same results as given
flipr=# select song_id from songs limit 5;
song_id
---------
945
946
947
948
949
(5 rows)

flipr=# select song_id from songs limit 5;
song_id
---------
945
946
947
948
949
(5 rows)

flipr=# select song_id from songs limit 5;
song_id
---------
945
946
947
948
949
(5 rows)

flipr=# select song_id from songs limit 5;
song_id
---------
945
946
947
948
949
(5 rows)

flipr=# select song_id from songs limit 5;
song_id
---------
945
946
947
948
949
(5 rows)

flipr=# select song_id from songs limit 5;
song_id
---------
945
946
947
948
949
I just want to know what exatly --"LIMIT without ORDER BY returns random rows
from the query" --means
Regards