fewer reshoots? when they film something, it's also shot on a video system so they can literally jump from the scene, and the director can show the actors seconds later.....you can even see this example in a lot of "making of" documentaries.
if we are comparing time it takes, when lucas shoots the film in digital he films it with a Digital HD Camera with tons of blue/green screens, and then spends over a year addding stuff. The principle shooting for Episode III was DONE in September 2003....
Um....the film gets to the theatre less than 24 hours before it goes to the public, sometimes even less. That gives us time to build it up (approx. one hour per print), and then screen it (and fix or order a new print if nessesary). When we do advanced screenings, the print gets there less than 2 hours before the screening....just enough time to build it up....did I mention that Security personel are watching this whole process for advanced screenings. Films arrive this late to stop pirating. The only time I've had a print arrive as much as 3 days early was "The Passion of the Christ" Lucas is VERY STRICT about his prints, they will arrive locked, with a code name (not star wars III) printed on the can.
if, by chance, you were talking about the printing process vs. digital copying than that's a different animal. the printing takes some time, but movies are done WAY before they come out in theatres, so that doesn't matter one bit.
The problem with digital (other than the contrast problems, color problems etc.) is that it's run off a computer. They lock up quite often, and they are not reliable (see Test Track). And as for the print degrading over time, they have spare prints, but the guys @ disney modify the projectors to be very gentle on the film. The only time I've seen a poor presentation was at the end of a Hall of Presidents Life cycle. They have replaced the print since (or maybe even to digital).
If you want to see how good a print can look, go to the Terminator atraction or It's Tough to be a Bug.
edit: and for those who think Lucas is done, he plans on making all 6 films 3D for an IMAX presentation in 2007 :-(