There's one structural difference: Usenet had no engagement metric but replies. Modern replacements measure and implicitly optimize for view counts (the lurker experience); both Reddit and Hacker News sort and surface posts based on a karma score/like count.
I think this difference led Usenet to implicitly optimize for high-effort posts. The stereotypical Reddit "in-joke" thread has no place on Usenet because the principal reward of karma is entirely missing. Instead, posters are implicitly rewarded with attention when their posts garner replies and discussion.
On one hand, this encourages real content and discussion over superficial "updoots to the left". On the other hand, it also encourages flamebait and high-effort trolling, which a vote-scoring system can silently suppress.