You're right. As of yet, slot machines do not accept credit cards. This very thing, in fact, is illegal in Nevada. Nevada Revised Statute 463.3557 states, "An electronic transfer of money from a financial institution directly to a game or gaming device may not be made with a credit card."
However, your timing is interesting, since a company called Cash Systems recently announced that, in a joint venture with Bally Technologies, it's developing slot machines from which players will be able to directly access cash from credit-card, debit-card, and bank accounts.
It's a touchy subject. As mentioned, it's prohibited by law. So the law would have to be changed, but that’s a political hot potato if there ever was one. Anti-gambling forces would have a field day. Even politicians in Nevada, where Gaming Inc. has enormous influence, would probably have a hard time justifying such a move to their constituents.
That's why the technology now being developed that will, one day, allow players to access credit-card and bank accounts right at the machines will not accept the credit cards themselves. (The acceptance of debit cards isn't specifically proscribed, but the moral question remains the same.) Instead, the systems will enable players to access funds by connecting the accounts to their players club cards. Thus, you won't be inserting a credit card into the card reader on a slot machine; instead, you'll be inserting a players club card and availing yourself of your money through it.
Does this sound like a fine point? It is and it isn't.
It isn't, because you can, currently, with just a little trouble (going to the cage and filling out a form) turn a line of credit from MasterCard or VISA into cash in a casino -- though, of course, you'll pay through the nose to do it.
It is, because insinuating the players club card into a credit transaction right at a gambling device could have a number of advantages, from both the casino's and the player's points of view.
From the casino's perspective, using the player's club card to access cash from credit and bank accounts circumvents the specific prohibition in the law against credit cards. So no law would have to be changed. Secondly, it allows casino operators to control credit that's funneled through player's club accounts. For example, they could, conceivably, cap credit at 25% or 50% of the line on the card. They could also completely shut known compulsive gamblers -- people who put themselves on exclusion lists -- out of the money-access system throughout the casino. And third, of course, opening an extremely convenient avenue for customers to access their cash right at the machine will, without doubt, accrue to their bottom lines.
From the player's perspective, they too get the convenience of cash access at the machines, without having to insert an actual credit card or bank-account data. Customers can also set up, beforehand, a credit limit that the casino will not and cannot exceed, no matter how much the customer begs and pleads in the heat of a losing moment.
Given that Cash Systems is in the process of developing the technology that would allow slot machines to accept credit in one form or another, this debate will no doubt continue for some time.
