I think the reason that is so is that the HN system encourages certain behaviors which lead to better discussions whereas the slashdot system is more of a passi

I think the reason that is so is that the HN system encourages certain behaviors which lead to better discussions whereas the slashdot system is more of a passive filter on a noisy feed, which is inherently a losing battle. HN survives mostly by being small, self-selecting, and somewhat obscure. Slashdot, for all its flaws, is remarkable for being large, well-known, and of consistent quality. Most comparable sites would be well on their way into the gutter at a quarter of /.'s age. I'm aware of only three viable means of maintaining stability in an online community: slavish adherence to the Peyton-Jones Law (viz. "avoid success at all costs"), iron fist moderators and a tangible cost to participate (cf. the Something Awful forums), or whatever secret sauce /. has. HN almost certainly doesn't have the third, and the Powers That Be have better things to do than implement the second. I seem to recall pg describing the slow growth of HN membership in very positive terms, so I'm pretty sure there's a deliberate strategy here.