Except without nested/threaded discussions. I don't know why the social web loves flat comments so much.

The circle of life... We're just in that stage of the cycle.

  while(true) {
    Start simple
    Add features
    Declare it too complex
    Abandon it and start again
  }

Flat comments ensure a narrative thread.

All too often they result in no thread whatsoever.

Like Twitter encourages? Or maybe you're referring to YouTube comments.

Okay, Twitter is more like a disassociated bag of nodes in a partially connected non-directional graph where half the edges don't connect to the node they're intended to connect to.

YouTube is a pack of raving howler monkeys with the occasional howler monkey researcher at the periphery. And, in fact, YouTube used to have threads, but they were still threads full of howler monkeys.

I'm talking more like your classic bulletin boards producing high quality content, like MetaFilter, Something Awful, and the like.

We agree on the sites, but I don't see what the conversation being flat has to do with it. Reddit is famous for the AMA threads, those are threaded.

Yeah, but try reading an AMA after it's been finished. It is really hard to find everything from the Askee.

I'm not intrinsically opposed to threads, but I'm not sure they're super beneficial outside of technical contexts or in an environment where people are expected to break a larger conversation off into it's own little set of discussions to keep the high level conversation easy to understand.

Narrative threads ensure a low signal/noise ratio and stifle natural discussion tangents.

I think it encourages a very high signal/noise ratio with the right moderation. eg whirlpool.net.au. Posters are encouraged to make their own threads, not go offtopic, etc.