> he doesn't mention Basecamp Next anywhere in the post
He doesn't need to; it would undermine the credibility of his message, and given 37signals' business principles, he stands to gain more by spreading FUD towards VC-backed startups in general than by plugging any one particular product.
/everything/ on their blog is a marketing piece. Nothing they do is altruistic. It either markets a specific product or promotes the brand in general. Part of that brand is lifestyle related - use our products and you'll be a successful small businessman/woman.
The term is enlightened self interest. Think of it like this if it is good for my customers and they all make money then they have more money to pay me. If I get my customers, who are largely start ups and developers, to believe my model, which is clearly working, works, then more people will use my product, and I will have more large clients working in the same space as my company is. Sure it is self interested, but it is also genuine and productive.