Motion pictures fall under the category of "works made for hire" and thus fall under corporate and not personal copyright; Lucas doesn't own the films, his company does, but he owns the company so he found a loophole to control them to his personal desires. Copyright for the SW films is owned by Lucasfilm LTD (and formerly Twentieth Cent. Fox for the first film). There was a pretty big copyright extension law put into place in 1998, which complicates things by dividing lines between before and after 1978, but it looks like corporate copyright is the same across the board.

Corporate copyright protects the works for 95 years (increased in 1998 by 20 years from the previous 75) from the date of publication. This means Star Wars will enter the public domain in 2072. Empire Strikes Back enters the public domain in 2075 and Return of the Jedi in 2078.

This is not quite as dramatic as 100 years, but at roughly six decades from now, probably most of us here won't be around to see it, and certainly no one who actually saw the films in their original release will be able to. I'm sure that in 2077 there will be a really big "Star Wars 100th Anniversary" thing where people will finally be able to show the original version with complete freedom. Maybe I'll be around, showing our fan preservation discs as museum pieces from the ancient days when rebel fans tried to keep the films alive using things like analog NTSC video copying and mail-order trading.