Casinos make money by providing games with various house edges to gamblers. Gamblers and casinos know this, and if it is unfair you have the choice to not gamble. Suppose there were a glitch with the machine that caused it NOT to pay out as it should... The casino would be liable to pay back that money to gamblers under numerous gaming laws. Would you then say that they should not have to pay it back as gamblers should assume risk when they gamble? Also, if it were found that the casino knowingly had a glitchy machine out there that did not pay out there would be people going to jail for that.
If there were a vending machine that gave me all of the money it had in it as change after hitting a combination of buttons, and I travelled to every machine in town and did this, I would be stealing. This is no different. If they calculated the house edge wrong and launched the game to players that would be a different story as the players played in good faith and it is the casino's fault that they did it wrong.