Well, the point is that a lot of people post their site on HN as "Show HN", and the "intended audience" is then (or should be) "power users", which should also mean that "power users" (few as they might be) are potentially interested to your site, but you make sure that only a subset of these power users can access your site (not necessarily in full, sometimes a simple text summing up what the thing is about would be enough to either - as I do if the page doesn't load - discard it or get me interested enough to turn javascript on/use the "other" browser).
If you don't post your site on "Show HN" the missing "no-javascript message" is only a (small) lack of courtesy, if you do post it, it sounds (to me) like a plain lack of attention.
In the real world, you open a new shop in town, and advertise on the local newspaper "everyone is invited for the shop opening tuesday at 7:00 P.M.", than you put at the door a couple big guys that only let in those dressed "black tie". I do have a suitable attire, but I am not going home to change into it, not without having at least the possibility to peek inside your shop and see what it is about. Will I become a customer? Maybe yes, maybe not, but more likely not.
1. You browse without JS. You're a power user. You already know why the page doesn't work. A courtesy message would be nice, I guess, but it seems fairly pointless.
2. Should my HTML and CSS still target IE7-friendliness? IE7 users still have more market share than actual humans who browse without JS. They get treated like lepers in the Year 0, and we all seem to be okay with that.
3. Well-designed use of JS can help distribute computation load that might otherwise all fall on the server. A very contrived-to-be-important (but fairly common) example of this is scaling/cropping an image before it's uploaded. Or, even though I have some other reasons to hate on SPAs, page rendering itself. The no-JS user is more expensive to serve than the typical user.
4. Except for some extreme cases of JS reliance, search engine spiders are a head and shoulders more accommodating to developers' choices than no-JS users are.
I just don't think that making accommodations for no-JS power users, who are not plentiful, and know full well how to turn JS back on, is valuable. Making JS bundles smaller and making them load more efficiently? That's a worthy cause for sure. But people who browse without JS at all are extreme outliers in the 1st world, and all of them know how to toggle it back on. Developing countries? If I were trying to serve those users I would do the research and make choices accordingly.