Just read some more Steve Denning

Middle-management resists...

 Middle managers have often built their lives and careers on mastering the hierarchical pathways of organizations. They can feel threatened by the emergence of new non-hierarchical work flows which no longer require command-and-control management behaviors.  Communities of practice are indeed less orderly than hierarchies and it takes time for middle-managers to understand that maintaining order can advantageously be replaced by facilitating and cheer-leading knowledge sharing initiatives.