It's not fear that makes Jason Fried/DHH avoid trying to build a really big business quickly. It's a lack of ambition. There's nothing stopping them from taking $10 million from VCs at ridiculously generous terms to try to build a really big startup. Like most rational people they're content to have good jobs and enough money not to have to worry about it.
This is why successful serial entrepreneurs are so revered. It usually takes extraordinary ambition to succeed more than once.
Nobody who sees the new 37signals office will walk away thinking "these people lack for ambition". I don't want to bicker about this point you're trying to make; maybe you're right and there's a different breed of ambition at work in the shoot-the-moonies. But 37signals is not just a "good job and enough money".
Judging a company's ambition by the size or grandiosity of their office is exactly the kind of thing Fried/DHH rail against.
Tons of companies build big pimped out office and justify it to themselves as being necessary for their future plans. It's one of the signs that you have "arrived".
This is why successful serial entrepreneurs are so revered. It usually takes extraordinary ambition to succeed more than once.