I took it to mean clearly delineated responsibilities (i.e. who gets blamed when a part / aspect doesn't work).
If there are unclear boundaries between responsibilities, things will fall through the gaps when one group assumes another will take care of something.
Furthermore, when people are held responsible for quality completion of a task, they are often more driven to achieve the task at-quality. This must be balanced with not over-taxing them, but that's a given.
If there are unclear boundaries between responsibilities, things will fall through the gaps when one group assumes another will take care of something.