Here's a question for you. Let's say you go and see a movie at your local theater and then a few months later, when the film is released on DVD, the DVD contains both the "theatrical version" (aka the one you saw) and the "director's cut" (a version which contains never-before-seen footage, some deletions of previous scenes and maybe even a bit of re-editing so that scenes occur in a slightly different sequence).
My question is, if the movie you paid to see at the theaters wasn't the director's cut, whose cut was it? For the last fifty years or so the auteur theory of film making has held that the director is the one, true creator of any given film. The director's status supersedes that of the screenwriter, the composer, the editor, the special effects technicians, the cinematographer and the sound engineer (among others). The director is king and has been for many years.
But if the director didn't "cut" the version of the film seen in theaters upon first release, who did? The producer? The studio executives? It certainly wasn't the screenwriter or any of the other craftspeople that worked on the film. Why not just let the director "cut" the film the way he or she wants it the first time and be done with it? Why not just one official version of the film for everyone?
The answer of course is money. There's money to be made by having a second version (or, in the case of BLADE RUNNER, eleventy-hundred versions) of the same film. This helps drive sales of DVDs and Blu-Ray discs and it also helps with any future theatrical re-releases.
The first movie that I can recall having a special "director's cut edition" was Steven Spielberg's CLOSE ENCOUNTERS OF THE THIRD KIND (1978). A few months after the film was released and became a box-office blockbuster, a tinkered with version was re-released to theaters that contained footage of the interior of the alien mothership at the end of the film plus a few brief new scenes here and there along with some deletions of previously seen material. Did it make the movie any better? Not really. The entire narrative and ending certainly weren't changed in any major way. I got to see some stuff I hadn't seen before and I had to pay to do it. The DVD release of CE3K contains not one, not two but three versions of the same film (the theatrical version, the special edition and the director's cut). I should know. The DVD box set is sitting on my shelf.