It's not only normal practice but a must-to-do. If you're gonna release a concert video the sound must be recorded "multitrackingly", so you could edit or re-record something what gone wrong. And when you edit video you must hide such things like scratching someone's nose, connecting plugged-out cords and so on. I always tell that filming is a half of magic, another half is editing. So, that fact shouldn't be shocking.
But it's interesting though to see sneak peaks of bloopers.