Yeah, they're gearing up to a new product launch. Is this supposed to be bad?
Besides, that only tells up that they post a lot of new content for their blog. Nothing about how this content is voted up on HN --which, I, presume, is simply by folks finding it relevant and upvoting it. Or, do you think that they have their employees doing the voting to their own articles. Because certain people certainly imply that. To which, I respond:
1) HN is a social news site for hackers, people vote on stuff the like, and DHH et co are popular in Ruby/Rails hackers to say the least.
2) HN is a social news site for hackers. You really think a company like 37 Signals thinks they'll gain something regarding new customers by having it's articles linked and discussed here, and so much that they'll devise such a scheme?
It is news when arguably a company that created the most well known web framework posts a blog entry titled "No framework needed". If you look for a TL;DR it would be "Use the right tool for the job. Do not be dogmatic about your technological choices."