I think most sites can be broadly classified as (1) "relatively static" such as hackernews itself, news/blogs, text-based sites in general, or (2) an entire program/application running in the browser, such as a game or collaborative text editor. Most sites fall into category 1 and therefore need very little JS to do their job effectively, but they come up with 50 different things for JS to do on their webpage, then spend time and effort optimizing and minifying instead of just not doing those things (or doing them in HTML).