Why don't they just tell us?

[rant]
With all the Kill Bill problems (HK and Thai) and plenty of other non information, I was wondering if there is any reason that we never know for certain what is on a dvd until we go out and buy it.

Press releases are not always accurate. In fact we have a huge advantage over the rest of the world by searching through the bbfc site to check for extras but even that is not conclusive evidence (ie Dumb and Dumber).

I imagine it takes many weeks to come up with the contents of a disc and they would have a complete disc ready long before production starts, yet it is felt unwise to 'leak' this info to people who are likely to buy the disc. So why the secrecy?
[/rant]