Its private property. The Gideons have no right to place anything in the hotel rooms without permission. If you are offended that they don't have the bibles there, either bring your own or stay somewhere else.
A large portion of the casino business is the attraction of foreign customers. They do everything they can to avoid even the slightest thing that will upset them. You should see what the Vegas hotels do to attract and keep foreign gamblers. Remember the giant lion at the entrance to the MGM Grand? Gone. Reason, many asians wouldnt visit the MGM Grand because they refused to walk through the door because of the Lion entrance.
Many of the "whale" suites will have an 5 chairs at the bar or tables because the number 4 is bad luck in some asian cultures. Other suites will have no books at all in them because they are seen as bad luck by some of their big customers.
You couldnt even begin to make up some of the reality in these suites to accomidate their visitors. If refusing the Gideons request helps keep their customers happy, then refuse the Gideons.