I'm still not sure where some get this idea that a billion dollars is somehow a benchmark for a sequel or franchise. Are they familiar with box-office numbers? Do you they any idea how much of a "lightning in a bottle" scenario it is for a film to make that much? Only 16 movies in the entire history of cinema have grossed that much.
Further, NO Marvel movie leading up to The Avengers even came near a billion...and I'd say that franchise is just fine:
All Worldwide Gross:
Iron Man (2008) : $585,174,222
The Incredible Hulk (2008) : $263,427,551
Iron Man 2 (2010) : $623,933,331
Thor (2011) : $449,326,618
Captain America (2011) : $368,608,363
In fact, Man of Steel is on pace to outdo ANY Marvel movie leading up to the Avengers. Again, where do some get this bizarre notion that a billion dollars is somehow a benchmark for sequels or a franchise? I mean, The Hangover "only" grossed $467,483,912 worldwide and has three sequels.
On a side note, The Dark Knight (2008) took 33 weeks to break a billion. Given that much time, who knows where Man of Steel will be.