I think Slashdot's and Reddit's problems run deeper than one-liners. /. has some features I think would be interesting to add to HN (meta-moderation is a very interesting concept), while HN has some interesting things /. would stand a lot to gain if implemented (the idea editors shot down stories rather than post them).
Whatever Slashdot's problems, they're still the gold standard in moderation systems, and something about that site seems to encourage long form comments- something I often miss here.
