The site is running as a cgi script, according to the article, and hitting the HN front page doesn't seem to have slowed it down in any way that I've noticed. So I think the point is well made.
(I am the author of the linked-to article and also the author of the software it's running. Said software also has (on-disk) caching, but that's not why the last-modified is back in December of last year.)