Ok, so maybe it's not PURELY leaderless...""

http://www.develop-online.net/news/44746/Valves-perfect-hiring-hierarchy-has-hidden-management-clique-like-High-School

"Developers were originally left scratching their heads when the hugely-respected game studio went through a round of redundancies in February. It was seemingly uncharacteristic as not only did it drop important staff members, including Ellsworth and Steam chief Jason Holtman - but the business is built to value and support all developers thanks to a flat management structure.
It even has a lengthy management handbook that explains how this radical operation uses peer review and colleague ratings to hire and fire individuals.
It was this mechanism which Ellsworth battled against to hire her own team - and which she eventually fell foul of.
Her frank account of what happened - detailing the tough side of Valve's idealised structure, how it betrayed her, and why its hiring process are flawed - is 90 minutes long and well worth a watch if you have the time, especially as it details how Ellsworth managed to retail ownership of the hardware ideas she dreamt up for Valve - you can view the first part here."

I wrote about Valve's non-hierarchical structure before, but here is an insider's look at who actually has the power in the company.  But I would point out that this is human nature. People have different personalities, including how expressive and aggressive they are.  OWS tried to make it easy for even shy people to have input, but still human nature puts the shy and quiet people in the back as far as management goes.  Democracy tries to get around that by giving every person an equal vote.  But if you have a management structure where everyone is supposed to be "equal" then don't expect that everyone will have the same amount of input, just because people are people and differences will show.