He didn't do anything that violated their terms to terminate an account and after all he don't really matter that much to the casino's perspective, he will be given attention only again if he needs help or violates the terms. Until then they have a business to run and it doesn't seem to be worth going after everyone who tries to bully/false accusations against their reputation.
You do have a point, but they could still pull the plug on him if he harassed them a whole lot more on their site when compared to his erratic and short-tempered behaviour with them on this forum.
There is always a limit to which casinos can put up with their customers basically.