It looks like they edited the two parts into a single movie. It was resubmitted to the MPAA, which is something they wouldn't have done if it was the two movies packaged together.
Also saw this on another board
"I found some information from the DVD product page at Wbshop.com. It looks like this version will have all the extras from the first 2 releases, plus an exclusive cast and crew commentary track, a 70 minute Frank Miller documentary, exclusive artwork, and 4 collector cards "