You can run around in circles moaning about how it isn't "fair", but it isn't the Mark Cuban who built the infrastructure or attracted the users with a core product on Facebook. Secondly, Facebook never guaranteed 100% reach, I'm not sure why Mark Cuban expects it (and for free!).
To be fair, he asked in his post for cost certainty, not "free."
Now, honestly, what I want as a user and as an advertiser is the ability for the user to turn up and down the volume of another entity, be it a person or brand. I may want medium on George Takei, high on King's X and low on Hormel's Spam (yes, I like Spam.) Do you think it'd be valuable to send things to different demographics as a brand? I know I think so, especially if I can get some cost certainty.
The problem is that the amount of likes and the value of the brand are unrelated. Takei is not going to pay as much as Quizno's, even if he has three times the fans.
I dunno, I think businesses realize that reach comes at a cost. In FB's case, however, they interpreted the cost as the time, effort, and resources that it takes to build a fanbase and pump out relevant, interesting content. Now they have to pay more to reach people who've voluntarily said, in essence, "I want to read/see your stuff." It feels a bit like a bait-and-switch.