As a backup, Vick is under no pressure to "prove" anything to fans and media (outside of proving he can stay out of trouble on probation). He responds best, both on and off the field, when he is not under fan and media pressure.
He'll stay the backup until Kolb gets back and starts sucking again, and then Reid, who no longer has McNabb to shield him, will put him in permanently to stifle the BooBirds. Vick will need to spread the ball around a little more (TE, second and third receivers) to be effective long-term.
~lw3