Lucas even said that the only reason they released the 2004 SE so early as opposed to the original plan of 2007 was because bootlegs were becoming so widespread. I think he may have included a similar statement recently regarding the OOT.
But i have no doubt that it IS because of bootlegers. Go to ebay--theres tons of copies of the OOT being sold for very high prices. Thats money that goes to Lucasfilm's pocket if they put out official copies. Additionally, they probably figure that since an official pressing of the LD master will be better than any possible LD preservation we can do, the fan preservation community will suddenly wither away since their efforts will no longer have any use.
Thats why this release is so balls. They dont have to put any effort into it--just dig up the Laserdisk master and put it out on dvd. Instantly, both bootlegers and fan-preservationists will be out of work (and yes, despite the amazing results of XO I am very sure, unfortunately for them, that the official disk will be somewhat better in picture quality). Tack on the original opening crawl as a bit of extra incentive and you have them. Everything is in Lucasfilm's pocket. All those people shelling out two hundred dollars for bootlegs will instantly fork out money for even better official versions at a fraction of the price (with no legal reprecusions) and once all the people who have waited all this time for the dvd have bought it--ie january--the release can be pulled.
I thought maybe Lucas changed his mind about "the films are dead" thing, but it seems he hasnt. The only reason its being thrown out at all is because he is losing massive amounts of money to bootlegers. So he throws out some half-assed version for a limited time and problem solved. I'm thinking maybe the OOT will never be properly archived for home video beyond the original Laserdisk D2 tape from 1993. Maybe our best efforts will be fundraising for a proper 4k scan of a 35mm print from a private collector (seriously).