I will put this under an LJ Cut to spare those who haven't seen or don't care:
Why didn't Peter just fly off?
I think Peter was primarily using all his focus to hold what control he was loosing over Ted's ability.
I think had he taken the time to concentrate on flying as well as holding down Ted's ability he would have entirely lost it.
I think the explosion going off in NY as originally seen might have been Peter trying to fly away when Nathan wrote him off.
Many of the exploding man pictures seem to show him slightly levitated if memory serves.
Nathan provides the flying, then Peter can spend more time slowing the loss of control.