I think a major point is that Peter Jackson wanted to release a shorter film in cinemas after being panned for the long length of Return of the King and King Kong, so material had to go, even if it was shot. e.g. the mother's affair with the detective was shot. That's why the detective has a guilty reaction when Susie's dad thanks him for his help. If you didn't know about the affair from the book it makes his reaction seem a little weird.
Peter has always taken advantage of the DVD format so he will likely release an extended cut, maybe even on the first release (i.e. not a 'double dip' unless the studio force it). I think it only neeRAB 10 minutes or so just to flesh a few things out.