It's a term of art that, in movies, means the big blockbuster that is going to put the balance sheet in the black, in the process allowing a lot of other smaller and more risky pictures to be made. It has taken on an analogous meaning in other domains.
When referring to an OS update, I assume it means the compelling feature(s) that will get people excited about upgrading.
It's actually interesting that you flagged this, because of course Jobs was involved in movies thru being the major investor behind Pixar, and he admired Disney. It seems to illustrate him thinking about parallels between the two mass markets of computers and movies.
