What really sets GitHub and to a lesser extent 37signals apart is that they are making a product for themselves. That's how they manage to only hire doers. They don't need marketing or usability testing or operations or acquisitions beyond what the doers provide because the feedback loop to the target market is near direct. That's not to say it's easy to do what they've done, but rather it's much less likely those principles could be held as the staple of companies in other markets where engineers and designers will not be as naturally adept at nailing product/market fit by themselves.