Do you take the same position when teams cancel contracts?Surely you see the difference in your situation and JJ's - his job hasn't changed, they're not asking him to do anything else he's not already agreed to do for X dollars.
Now he's decided he thinks he's worth more and refusing to do what he agreed to do (for a crap-ton of money, no less) unless they will renegotiate for even more money.
It's disgusting behavior - and I don't care if it's common or not. He's showing that greed is a stronger part of his character than his word, and that's sad.