I don't think that this is related to MPAA rating. AvP got a PG-13 certificate. Paul Anderson is just looking over and over again the movie, to make sure that everything is okay. If he finds some problem, especially CGI related, then he will correct that! It's a good thing that Paul really takes his time on the movie.......I would rather see a finished product, than a unfinished product on the 13th.....