It'd probably be interesting to do a historical analysis of this, I think Stacker News probably follows a pretty extreme distribution of (1) lurkers vs. (2) sharers vs. (3) producers and specifically has a lot more of (1) then (2) since people vote with their sats.

Putting my microeconomist hat on, the fact that a post costs 100x more than a reply basically creates the incentive for threads that are more packed than the norm. For example, HN (the place that must not be named) doesn't typically have a lot of discussions - but then upvotes and replies are "free".