Well, fixing them might be harder than you'd think without a front end rewrite. HN is built with tables, last time I looked...
Last I looked, hn was built with functions that wrapped primitive/direct generation of html... I can't imagine it'd take that many replacements to change the structure to use a hierarchy of paragraph-tags or divs (ironically that might also be easier to style with parent-child relationships...).
But I didn't look very hard at the code last time I looked.
I'm not sure why nothing's ever done about it -- style aside hn has three serious usability problems: non-wrapping text, hopelessly small voting widgets ("up", "down" text buttons/links would be an improvement) -- and the comment box on mobile/small screens.
Am I correct in my understanding that there isn't a (current) public repo where one might suggest fixes for this? I really do enjoy the utilitarian "feel" to hn, but these long-standing issues really need to be fixed, and at least fixing the first two is quite easy.
[ed: by "plain html" I mean not simply wrapping the page in a table, and allowing a more normal view. Technically one could use the table markup and just change the css too, of course]