I think his point is that the critical failure of these films will affect the box office of the NEXT film in the series. Using Pirates as an example, I was underwhelmed by the 2nd, so I never bothered to see the 3rd. It's not like the theatre gives you your money back if you dislike a movie. So while POTC3 may have had a high box office, there are likely a lot of people who paid to see it, disliked it, and won't pay to see the 4th. That's really the entire underpinning of the franchise movie system - trying to build box office momentum so that your flick isn't tied completely to reviews/word of mouth.