Unfortunately, that's a design problem for Hacker News in general - people will be here for years and not notice features that were right in front of them.
Yeah I’ve been a member 2 years and lurker much longer and only last week I worked out what “prev” and “next” do.
That might say more about me than HN tho :)
I didn't see prev and next buttons until a few weeks ago. It's possible that I was just blind, but I think that they and the "context" button are new.
Yes, root, parent, next, prev, and context are all pretty new.
There really aren't many buttons, we've just stopped seeing.
People have also not noticed the thread folding link after it's been there for a while, or the fact that the site has a footer with links. It's difficult to notice things in a grey-on-grey color scheme.