With the money both teams have they can afford to sign better players, and will tend to have the best teams in the league. There is obviously going to be less penalty opportunities in either teams box, than in the oppositions.
Having said that, other teams will still mount attacks from time to time and will get into the oppositions penalty area. I would need to see any incidents that should have been penalties against Celtic.
I try to be honest, and if I genuinely feel Celtic should have conceded a penalty I will admit it. Off the top of my head, I can't remember any controversial calls that have gone in Celtic's favour this season.
I do remember a game at Hampden against Kilmarnock in which I felt Killie should probably have had a penalty. I'm a bit old school, and I felt the Killie player went down looking for a penalty after he was held but, as we have seen in Rangers games, these days a slight tug on a jersey is considered a penalty, so we definitely got off with one there.