There is no way to prove you actually legitimately own an old copy on an old format, and will dispose of the old copy.

For retailers, a trade-in program would likely cost them more to administrate than you'd get on a discount.

For the studios to do it over the mail, the cost there also could negate any savings.

My grandfather told me that when he was 21 you either had live music or sang it yourself. He was amazed and astounded by the likes of stereos, LPs, and black & white TV. I'm guessing if he had lived long enough to see personal computers and my IPod it might have pushed him over the edge. 20 years from now when my first grandchildren hit 21 I can't wait to tell them about what we had to put up with in 2007.

Do it yourself. Buy a burner and a few stacks of blank discs. Find yourself a good ripping/burning program and systematically rent (via Netflix or local video store) and burn all the movies you once owned on old formats. For further efficiency, I recommend buying CD envelopes for easy labeling of your discs and CD-width boxes for storage. This method isn't exactly free (or legal), but companies whose sole purpose is to turn a $0.03 piece of plastic into a $14.99 product are NEVER going to upgrade your discs for free.