"Besides being small, 37signals has always been a flat organization."

..

"We've experimented with promoting a few people to manager-level roles."

So they are flat, with no chief anything, but they have 'manager-level roles'? Am I missing something or is there a contradiction in his description?

Edit: Got it, 'experimented' meaning that they tried, didn't work, and they went back to flat. Thanks for the responses.

Besides that I find that even with no job titles or formal roles, people within a company tend to self-organize and take on de facto roles. The only difference is that it isn't formalized, and people who end up managing aren't being paid manager salaries or getting manager options.