Supply and Demand
To be honest it really comes down to basic supply and demand. Yes some previous organizations overpaid and went backrupt because of it, but the UFC won't be able to rely on this forever. MMA is bigger than the UFC, and when more well run companies like Strikeforce come around the UFC will have to pay more or risk losing their stars.
It's already happened with Hendo and Fedor, and might happen with others in the future. As long as Strikeforce can balance this with revenue growth, they will be in it for the long term. If they pull an Affliction and basically try to outgun the UFC from the start, they will get trampled. But that's not what they are doing, they are attempting to seperate themselves from the UFC in many ways.