IMHO, yes....if they felt that the threat was far enough away from him...and I read that the security detail assigned to this innauguration is UNPRECEDENTED.
Even if they felt Bush was save, would they have Cheyney in the audience as well?
Arthur beat me to it....Cheney is there...and his absence from this could easily have been "excused" had there been a real threat...unless, of course, the threat is "no threat" outside of MA.