We need to put together a team of experts to audit all of these machines.
There were a few jurisdictions, Iowa and New Jersey come to mind, that were already aware of the nature of these machines and required the manufacturers to have their software audited and validated by (state approved) third-party gaming labs identical to what the slot machine companies do when getting code approved for release.
The key point was that the probability of a win couldn't be adjusted on the fly to make the target payout percentage (kind of what the article says). The probabilities had to be fixed for every player on every game. Although the first method is a lot easier to write, software-wise. =)
For the rest of the jurisdictions, the default payout was 40% and anything was fair game to hit that number. Remember that the next time you're in a Chuck E Cheese.
For every play of the game, or across all of those game machines sold?
It is the thing that makes it not gambling. In a casino, there is the risk of spending more than your disposable income, hoping to get your money back. In an arcade, you know that once the money is in the machine, it is gone, less chance to overspend. The main point of anti-gambling laws is to prevent addicts from ruining themselves, not to prevent you from spending some money to have fun at the casino, and not to save your disposable income.
The line is blurred when the prize has resale value, and in fact, a common way to disguise gambling is for the machine to give out prizes that the shop next door conveniently buys for a good price.
Legislation vary wildly, so I suppose they are legal in some places and illegal in others.
[1] https://gizmodo.com/how-one-perfect-shot-saved-pinball-from-...