IANAL, but it's possible that these users are now liable to pay for the extra games. They knew that the code was only usable once, yet used it multiple times. EA might ask for the games back or charge the users.
(I'm not taking EA's side, I'm just pointing out some possible consequences.)
If they did try to charge for the games they would get enough chargebacks that they would have a hard time processing credit card payments for a while. And with chargeback penalties they might actually lose money.
The only sensible options are a) do nothing or b) revoke games purchased with these codes. If I were them I would do nothing and treat it as an unplanned pricing experiment. Since a lot of these games have an online component (network effects!) the "giveaways" might increase real sales overall.
Even if that's the case, it would be unwise for EA to pursue this money. All anyone would have to do is issue a chargeback - which by the way incurs penalty fees for EA. More than that, it costs $25 for EA to file a challenge to a chargeback, making it completely not worthwhile.
Going after this money would be a PR disaster, a legal quagmire, financially negative in all likelihood, and permanently damage their relationship with their payment processors.
I would instead invest more money in hiring proper architects.
I would think that the transaction was perfectly legal, and that EA could in no way force people to pay for the games. I wouldn't however, be opposed to the idea that EA could revoke ownership of any subsequent free games obtained once the code had been successfully used, but it would be a PR nightmare if they did.
EA's only reasonable option is to eat the loss and write the cost down as a "lesson learned".
Isn't there precedence to this? For example, cases where Amazon priced something wrong and people bought at that price, even through the the price was almost certainly unintentional. I would think Amazon would have been obligated to honor the bad price until they discovered and changed it just like companies are on the hook for honoring mistakes in ads (although I think they might be covered by disclaimers these days).
How so? EA can flip a switch to remove the games, and claim there was never a valid license. As long as EA honors the orginal terms of the coupon, I don't see how the "cheaters" were wronged.
My point was simply that the legal situation differs significantly from the standard "You stole it give it back". Pretty sure most of it would be uncharted waters, so EA removing it with a flip of a switch is essentially a throw of the dice. EA would probably win as you say, but I suspect they'll let it slide because its too much hassle & bad PR.
(I'm not taking EA's side, I'm just pointing out some possible consequences.)