I think the main point is, 37 signals runs a bit like a lifestyle business - agile, low stress, no overtime; because that's what they think is the most profitable way to run a software business. Even if they wanted to do overtime, or were in a more cut-throat niche (i.e. taking on Facebook) they would run their shop the same way..

They aren't doing things the way they do because they think it's glamorous, or because it's easier.