Real quick: you know how BSDs were supposed to have "core bit" for "core committers"? If one was "on core", he could issue "cvs commit". Everyone else had to e-mail patch to one of the core guys. One problem with that setup was that people are weak. A core guy could be severily tempted to commit something that was not rigorously tested or otherwise questionable.
OpenStack addresses this problem by not actually letting "core" people commit anything. I'm on core for Swift, but I cannot do "git push" to master. I can only do "git review" and then ask someone else to approve it. Of course, this is easy to attack if one wants so. For example, committers can enter into a conspiracy and buddy-approve. It's possible. But at least we're somewhat protected against a late night commit before a deadline by a guy who was hurried by problems at work.