The problems only start once the "tribe" grows beyond 150. That's when the number of people involved is too great for the human brain to process the entire social network. Hence why formal organisations and hierarchy are now needed.
It's great that startups and small companies are innovating with different organizational styles. Many of the structures found in big corporations are overkill for small organisations where everyone knows each other. Just don't expect any success stories from these startup experiments to scale up to bigger companies though.