At least at Google, middle management doesn't exist to run projects. They exist to provide career guidance, ensure people are happy, and keep them from leaving for Facebook.
This is a task that doesn't scale, because it requires knowing your reports well enough, as a person, that you understand their career goals, their likes & dislikes, their strengths & weaknesses, etc. so you can steer them into the right role. It's the tech lead's job to manage the (engineering half of) the project, and the tech lead frequently doesn't manage any of the people involved. I've found that managers can rarely manage more than 20 people effectively, and usually drop off sharply in effectiveness after 8-10 people.
Open source projects don't face this limitation, because your way of ensuring that everyone's happy is to assume that everyone who's not happy has quit. I suppose some big companies do this too - Yahoo seems to be trying out this strategy right now - but it really doesn't go over well with the public at large, and it wastes a lot of effort spent investing in new employees.