They don't.
The difference is that the Vegas casino catches this problem in its infancy.
And in the cases of severe errors they are caught on the first or second tax form sized result. In this case the bottom of the paytable was the problem so it might take longer than normal to be discovered.
There are other safeguards to casino errors on machines here. For instance, if a game had a mistake like this in a brick and mortar casino, the game would be locked up by professionals because if they don't lock it up, someone else will. That alone becomes something the casino will become interested in. And many other safeguards.
Another thing to consider is that you can cash tickets as you go in las vegas. You are guaranteed to get out a certain percentage before they shut the game down.