HN is often slow due to load issues; at least it has been that way in the past. What makes you think it's intentional?
I log out and it speeds right up. Could it be a logged in-only problem? Not sure.
Could be. Maybe it's not optimal code dealing with all the user details. It has to know all the submissions you voted on and anything else.
Or maybe it was a coincidence and it was faster at the time you logged out.
Some sites (possibly hn too) do not display cached pages to authenticated users. This could be the reason you see a decrease in response time compared to when you're logged in.
Why is it that most ASK PG questions are never answered by PG?