There was extra interest in TDK due to the death of Heath Ledger. I'm sure that fact was partly responsible for the large opening-week numbers.
That much is true.
Less obvious, given the interest in his death, was that Ledger alive was an additional draw for the "Batman Begins" sequel. His star was very much on the rise in the business, and this is another point that the HitFix writer mentions as regards actors like Saldana, Pine and Quinto: when a big successful film stars relative unknowns who then go on in the next few years to become big names that boosts the likely box office of any sequels that those actors participate in. Another reason that Paramount is feeling pretty positive about the Franchise; they believe they've got a couple of career winners in this movie.