One of those arbitration sites (AskGamblers or Casino Guru) doesn't investigate cases that involve sportsbooks. TrustDice has a sportsbook. Since they won't be investigated by the arbitrator, they are free to make their own decisions. The other arbitration site doesn't investigate breeches of terms and service. Are you getting a clearer picture? You confiscate someone's money with silly accusations that they were involved in late betting (proven to be false and a lie in the resolved thread you linked to), you mention breeches of terms and service agreements and arbitrators won't look into the case. Since they have decided not to respond to scam accusation threads on the forum, there is very little that their victims can do.
This is a very informative details about the limitation of some trusted arbitration website that fights casino scam. In this case Bitcointalk is perfect on handling cases that involves casino with sportsbook.
The only problem that Im seeing on cases like this was if theres no hard evidence can be show while the casino choose to become silent, A single or 2 DT opinion will not gonna matter especially if the casino is backed by user here that benefits on signature campaign. This is the only unfairness I can see when someone fights against a casino that has great influence here.