Like many people, I thought Kathleen Sebelius was primarily responsible person for the botched roll out of HealthCare.gov and she should have resigned last Fall. You hold 'political appointee' as the responsible person for a political fight and she was that person.
She stuck with the task on hand and President allowed her to get her job done well. She did it and that is a perfect time to exit honorably. That demonstrates capacity of this White House to accommodate folks to try faithfully to repair a botched job. It is no less a good thing that the incoming appointee is a competent manager. This administration needs managerial competence in days to come since legislatively there is nothing what President Obama can achieve. What is left is to guard what policy enactments have erected so far.