This was first revealed shortly after Revenge of the Sith hit the cinemas, around the same time the new Clone Wars and upcoming live action TV series were announced.
At the time, McCallum said some tests had already been done on a 3-D version of the opening scene of ANH - I'm guessing they weren't entirely happy with the results, and put the idea on a back burner...
George Lucas is set to re-release the six "Star Wars" films in 3D, beginning in 2012 with one film annually led by "The Phantom Menace
Though the 3D versions have been rumoured for some time, Lucas was evidently waiting until there were enough 3D screens available to make the release a sizable enough event.
Fox, which released all six of the original "Star Wars" films, would also release the 3D versions.
"The Phantom Menace," originally released in 1999, would be first out of star-dock in the early months of 2012. After that, each of the films would be released in order at the same time each consecutive year, depending on how well the first re-release does. That means the original "Star Wars" and its sequels won't start rolling out until 2015.
Each conversion takes at least a year to complete, with Lucas personally overseeing the process. He has said that "Avatar" convinced him that "Star Wars" was ready for the state-of-the-art 3D treatment.
Also pushing the timetable is a potential breakthrough in 3D television technology. With Samsung penetrating the market with 50,000-plus 3D-equipped televisions and Sony sending its version to market in recent months, the home-viewing experience could be primed for 3D DVD versions of the classic films by the time the new 3D series runs its course.
http://uk.news.yahoo.com/22/20100929/ten-uk-starwars-5fdf947.html
THat's because they can't. Cameron was wise to use enourmous depth of field, it makes 3D work. A shallow depth of field makes a picture already look three-dimensional without the 3D glasses. Just watch Alice in Wonderland in 3D. It wasn't shot for 3D and when we see the nice close ups with little depth of field, 3D just doesn't work... because it already looks 3D.
I've been with some 3D video tests during a concert an couple of months ago. And the only shots where 3D really works, really makes the shot dynamic and deep is where there is lots of depth of field. So wide angles, everything in focus... that's what you need to create stunning 3D.
It is kinda limiting cinematographywise though...