They should have just smiled at the naysayers and went on with their day. To post an entire article on the negativity of one community seems unfocused. My only question is: why?
Disclosure: I'm a big fan of 37signals. This is kind of a surprise.
It isn't even the negative of one community, but rather the negativity of a small group of people within that overarching community.
People need to realize that sources of content almost always come in waves here on HN -- when someone makes an erudite post that makes it to the front page, there are a lot of people who will watch that source looking to repeat that success. And then you'll get the voters who'll vote it up just because it's familiar, until it becomes too familiar when they'll vote it down for the same reason.
We've seen these come in waves over the years (I've used HN far longer than this account). Coding Horror, Daring Fireball, Marco.org, Scott Adams, Dustin Curtis, etc. A small amount of very good content, and then lots and lots and lots of turgid waste that makes the front page simply because the author once did.
Personally I wouldn't include Coding Horror on that list and I am curious why you would. Almost all the content seems very objective and insightful compared to others on your list who sometimes can come across as Fox/MSNBC political show hosts.
Disclosure: I'm a big fan of 37signals. This is kind of a surprise.