No, the changes go back as far as 1977. It's just that in 1997 the most changes were made. And, obviously, those were the changes which were trumpeted most loudly by Lucasfilm.
It surprises me, though, that on a forum such as this, where fans will pick up on anything and everything (from colour coding to the different fonts used for the subtitles), no-one appears to have noticed the dialogue change that I mentioned. Or has it become de rigeur to just post endlessly about the changes that we don't like? Perhaps that's why the audio cock up with the music during the Death Star battle on the DVD of A New Hope drew so much stick and yet, when Matthew Woods changed it back to how it was originally, there was barely a murmour.
I blame the papers! Appeal to the lowest common denominator by selling bad news and people begin to believe that that's what they want to talk about. The endless negativity is rather wearing, though.