HN isn't the 2016 web at all. Not that you fundamentally need JavaScript, but HN's HTML hearkens back to the pre-CSS table-driven web.
Yes but when visiting a website with JS turned off, the site can still be progressively enhanced similar to how an electric stairs still works when the power is switched off. Users of the stairs still get to climb it, but now they have to put in extra effort.
It can, but sites often don't test that path (if they develop it at all), because it only applies to people who intentionally disable JavaScript.
Once upon a time, screen readers and similar accessibility software didn't work well with JavaScript, so better sites would pay attention to that case for accessibility. However, screen readers work fine with standard browsers and JavaScript now, which makes the "JavaScript disabled" case an incredibly tiny fraction of web users. (In fact, Mozilla found a few years ago that there were far more users with JavaScript accidentally disabled than people who actually wanted it disabled.) So, handling disabled JavaScript by just saying "you seem to have disabled JavaScript; you should fix that" really does seem appropriate for the proportional amount of time worth spending on that tiny subset of users.
That said, know your target audience. If you're building a mainstream consumer product, the proportional amount of time worth spending on running with JavaScript disabled rounds to zero. If you're building a product catering to a smaller subset of users, and you expect people with JavaScript disabled to represent a much larger fraction of your potential users, by all means take the extra development time to make that case work well.
Some news organizations implement their paywalls with JS. It gets rid of a lot of annoying ads and scroll-behavior modifications. It actually makes some sites subjectively better.