Captain Antilles said:

Plus, after all the years he (and his team) has dedicated to this project, why would he ever put out anything less than his final, ideal version? It would just lead to a mess--the near-finished cut would most likely spread around teh interwebz and probably get confused for the final cut for quite some time, perhaps indefinitely. After, once it's out there, it can't be taken back. It's better for him just to wait and put out one version.

For everytime we get asked this question....this is the best answer I've ever read.