Rework: Unveiling the cover
37signals.com
37signals.com
It clearly not aimed at their fans, but a much broader business crowd.
But I still think you're right: this is a book for people who buy business books in airports and read them on planes. Which is where 37s probably needs to be heading - my dad wears a suit to work and has never heard of them, but I think he'd get excited by some of their ideas.
Also... the comments there are crazy. People falling all over themselves with praise.