You know, I'm reminded of Universal and Charlie Mintz trying to put the Disney Brothers over a barrel. Universal thought by virtue of their contract, and by signing all of Walt's artists (save Ub) Walt would have no choice but to make cartoons for them.
We know what happened.
The problem with dealing with "creative" people is that the "project" becomes more important than the "money." I'm sure the Disney corporate believes that the Weinsteins shouldn't complain, Disney has made them a lot of money. And while that's true, that money may not be enough for the Weinsteins to compromise the "project."
They build a studio once. And if they have the resources to buy out Disney, they have the resources to start over (if Disney doesn't agree to a buyout, and they still want to leave). It would be a gutsy move, but they didn't get where they are by being cautious.