I dunno, the latest theory I've been working in my head about all the SE and other changes Lucas has been making to the movie is something along these lines:
Every change they make costs a ton of money to look make it look like it fits, so they choose their shots very carefully, focusing on the ones the average viewer is going to notice, rather than a frame by frame Star Wars geek like one of us. ; )
Still, one wonders why they didn't just make all the radical changes all at once, but perhaps Lucas was afraid of going TOO FAR and losing the audience, so he'd rather spread out the changes to get people to accept them, then make more later, etc.
Or it could be that they just aren't that meticulous, and he just does it every few years so he can have a good excuse to sell everyone another copy of his most famous products. But I am thinking it's just cheaper for them to focus on the shots that are most obvious first and foremost.