The latest word from Tokyo Game Show 2008 is that only the first batch of Final Fantasy Advent Children: Complete releases will include the Final Fantasy XIII demo as a bonus. That means that if you want any chance at all to play the demo, you'll probably want to pre-order the Blu-Ray movie from various online shops.
There is no extra cost, the first releases are not considered as "limited editions", Square Enix has simply decided that the demo will only be inside the first batch. The first releases will probably run out in a week or two, so be quick!
