Shouldn't .pgpass work with anything which uses libpq?

(Using PostgreSQL-7.3.1)

I noticed that the new ~/.pgpass password file works with psql but not with
my pgtclsh scripts, and I'm wondering: shouldn't it work with anything
built on top of libpq?

Digging into it a bit, I think no conninfo-based connection method will use
.pgpass, including libpq PQconnectDB() and libpgtcl "pg_connect -conninfo".
I think it is happening because .pgpass is only read if the password
argument to PQsetdbLogin() is NULL. But if no password is supplied in a
conninfo string, then "DefaultPassword" is used - this is an empty string,
not NULL. Am I right? Is this behavior wrong?