An important distinction for Usenet and 4Chan is the lack of a front page. Sure - there were bitter trolls all over usenet, and there were corners full of fire. However, it was necessary to seek them out. There was no algorithm that would hold them up to the light if they got enough traffic. That's enough to set Reddit apart - the fact that an eyesore can be brought out into the shining light through activity alone. It incentivizes trolling and disruption far more than either 4chan or usenet ever could.

This leads to the stratification you describe: the thugs can hang out in their own private Idahos until they feel like setting off on an adventure. The lack of friction between subreddits is something else unseen on usenet or 4chan - there remains a 'homepage' to exploit and if you exploit it enough, you exploit everyone's homepage.

Control of Reddit is fully in the hands of the VCs now. You've got Ellen Pao (ex-Kleiner Perkins), Sam Altman (Y-Combinator) and Alexis Ohanian (Y-Combinator) in direct control of five dozen untenured, unempowered serfs. When Marissa Mayer bought Tumblr and said she wouldn't fuck with it, people believed her; when she burned Tumblr's community into a gif engine it was immediately obvious that Tumblr's monetization strategy was immune from its community.

I suspect Reddit is in a similar place.