The thing that's so amusing about all this is that Chris Nolan's original "Batman Begins" did NOT even crack the Top 20 weekend openings in comic book movies.
Both "Fantastic Four" films, yes even "Rise of the Silver Surfer" made it ahead over BB.
So when analysis were projecting how "The Dark Knight" would be based on BB's performance, they were projecting around FF or maybe the lower end of the X-Men numbers.
But to have a franchise jump from #22 in "Batman Begins", all the way to #1 in "The Dark Knight" is something really no one foresaw.
It wasn't until Heath Ledger's death that drove the masses to see the buzz about "Ledger's last film before he died". Ledger also had the mass appeal of women from his chick flick days (something Christian Bale doesn't have) which I think to this day, TDK still holds the record for most female audience in the movie theaters for a comic book film at over 50%. Of course, TDK was also a good film that gave itself legs which drove more and more people to see it.
You also have to remember that Warner Bros re-released TDK twice. First on November 14, 2008 and then again on January 23, 2009 and ran it all the way until March. So TDK was around for almost 8.5 months straight in theaters. Both re-releases was what pushed TDK from $996 million and bumped it up to a cool $1 billion.