people have the tendency of to not quote what they are responding to.

Which they shouldn't (when they're not replying to a specific point in a long post, anyway), since we have a perfect archive here. Even if you read a reply to a post 4 year old post written 3 years before you ever first visited the site, the context is still available. Quoting offers much less on PerlMonks than on Usenet.

The UI of Perlmonks makes it so much harder to [keep track of a thread] than for instance on Usenet.

I do agree. Which is funny since the information is there - unlike on Usenet, where it depends on a lot of factors whether you will have the full context of a post.

Maybe it should be an option to always show the parent of a node you're viewing.

Makeshifts last the longest.