Petraeus was already over the Afghanistan command at CENTCOM HQ. Its natural for HQ commander to temporarily takeover until they find another field commander. Besides, such an announced tactic will resonate with world perception. I highly doubt that Petraeus is going to be the day-to-day guy in Afghanistan for a lengthy period of time. He has able commanders that work for him. That is how things work.
It's not what BO said, and you don't need Senate confirmation for that sort of thing. I'm not sure it's needed for an assignment below unified and specified command leve. Plus the service chiefs.
But Obama said it did, and The Won cannot be Wrong, so it must.. right?