Forrest Wickman notices the trend in films in which implosions are replacing explosions:
When the opening action set-piece of The Avengers ends with the destruction of a remote research facility, the structure goes out not with a bang but more of a cool sucking noise. Meanwhile, in the first trailer for The Dark Knight Rises, Bane is set not on exploding a football stadium full of thousands of people so much as imploding it. In the second Dark Knight Rises trailer, released last week, rather than sending a bridge up in a fiery blast, a few tactical detonations send it neatly collapsing into the water. We appear to be entering a boom in Hollywood implosions.
His theory as to why:
It evokes the most indelible image of 21st-century destruction, the one filmed on September 11, 2001. The most frightening visual from that day was not the planes exploding into the towers, but the towers falling in on themselves.