Here it is; because that's how the universe works.
That decision doesn't get made until "something" checks it/depends on it/interacts with it (the English language, at heart a way of telling macroscopic monkeys about tigers and bananas, does struggle a bit here). If you go digging yourself, you'll be able to go as deep as you like. I apologise for not presenting a better answer, but I'd really be doing you a disservice.
Edit: It's really not a good answer at all. I'm digging through old reddit threads to see if RobotRollCall ever talked about this. Her explanations were generally very accessible.
I asked the original question and I've harassed people with this question enough that I vaguely recall the answer.
In terms of the boxes, the answer is you wind-up breaking open the boxes over time in different ways that wind-up with being incapable with the perspective that "just" a black stone or "just" a white stone is in each box.
http://en.wikipedia.org/wiki/EPR_paradox#Mathematical_formul...
Because, when you put the white stone in one jar and the black stone in the other, it's decided. One of them does contain a white stone. One of them does contain a black stone. The universe "knows" which is which. The decision has been made.
With the entangled particles, it's not decided. You separate them, and you do NOT have one particle in "up" state and one particle in "down" state. That decision has not yet been made. It's not the case that one of them is "up" and you just haven't checked yet; one of them is not "up". One of them is not "down". The decision has not been made. One will be "up" and the other "down" when the decision is made, but that random decision has not yet been made.
You then move them a long way apart, and look at one of them; the decision is now made for BOTH of them, even though they're very far apart.