It's possible they were extra vigilant about tracking those prints in 1997, and making sure they were all returned. (Or proven destroyed if too worn out.) There were cases of Jedi prints being stolen from projection booths back in '83!

I could have sworn I've seen at least one SE print pop up on Ebay in the past five years. Might have been a single reel though. The DTS soundtrack CD's do show up once in a while, but they're only good for coasters unless you have the print and your own movie theater. ;)

Curiously enough, single reels of ROTS seem to pop up every month or so. They all have been from the end of the movie, and somebody usually bids on them. Where the heck are those coming from?