I think a lot of that fellow's auctions went for such high amounts because they were clean copies that had the boxes. The boxes certainly can add a big premium. I think for those who want to play the game, a loose cart or cart+manual can still be had at a reasonable price. Heck, I sold a complete boxed copy for about $67 or so on ebay within the past year if I recall...
These auctions really make those custom cases all that more attractive as an option for those who still want a complete look to their collection but don't necessarily care about the cardboard boxes....