Re: How to get the commitment?
Pointing out and blaming a person in front of the rest of the team is a dead-end and it will get your managers motives nowhere on the long run.
In my opinion, your organisation should commit to the fact that you are using Scrum as the development process and hence, promote and support self-organising teams as the way you organize.
Self-organising teams challenges the behaviour of the team members as well as the behaviour of the managers. It calls for awareness of "what kind of team are we?" and "how mature have we yet become as a team?" and constantly accommodate the leader interventions to the stage of the maturity of the team.
The people involved should think of themselves as an integrated part of the team instead of individuals working in a group. Mutual accountability is the keyword, so if someone has made a mistake, then the team as a whole has a problem.
You might find it useful to do some teambuilding exercises in order to form the team and make the commitment grow. I have published an article that explains about appropriate leader interventions and gives some practical suggestions on exercises you can do with your team. See: http://www.scrumalliance.org/articles/98-coaching-scrum-teams.
Hope that you find this useful
Bent Myllerup, Scrum Practitioner, Certified Systemic Coach and PMP