Composite primary keys

I tried to throw some invalid SQL to PostgreSQL and found its reaction
confusing:

$ psql test
psql (8.4beta2)
Type "help" for help.

test=# CREATE TABLE t1 (
test(# id serial NOT NULL,
test(# name text NOT NULL,
test(# PRIMARY KEY (id)
test(# );
CREATE TABLE
test=# CREATE TABLE t2 (
test(# id int NOT NULL REFERENCES t1,
test(# language char(3) NULL,
test(# txt text NOT NULL,
test(# PRIMARY KEY (id, language)
test(# );
CREATE TABLE

Here's my first gripe: PostgreSQL accepts this silently instead of complaining.

test=# INSERT INTO t1 (id, name) VALUES (1, 'text 1');
INSERT 0 1
test=# INSERT INTO t2 (id, language, txt) VALUES (2, NULL, 'text 1 no language');
ERROR: null value in column "language" violates not-null constraint

And here's my second gripe: although PostgreSQL correctly rejects the
INSERT it just has ignored my NULL specification.