Row IS NULL question

I'm playing around NULL. Docs says that
"A row value is considered not null if it has at least one field that is not
null." and "SELECT ROW(table.*) IS NULL FROM table; -- detect all-null rows"

So, I try:

wow=# \d tst
Table "public.tst"
Column | Type | Modifiers
--------+------------------+-----------
a | double precision |
b | double precision |

% echo 'SELECT count(*) FROM tst WHERE a IS NULL AND b IS NULL;' | psql wow

SET
count
-------
6
(1 row)

But ROW() IS NULL doesn't find anything:
% echo 'SELECT ROW(tst.*) IS NULL FROM tst;' | psql wow | grep 't'
% echo 'SELECT count(*) FROM tst WHERE ROW(tst.*) IS NULL;' | psql wow
SET
count
-------
0
(1 row)

What do I do wrong? Version of postgres - today's HEAD.

--
Teodor Sigaev E-mail: teodor(at)sigaev(dot)ru
WWW: http://www.sigaev.ru/