Blackjack already has a reproducible flaw, it is called card counting. It is not illegal, but casinos frown upon it and often ban people who are suspected of card counting. I would argue that noticing and exploiting a flaw in the blackjack card shuffler falls along the same lines. You are using meta-knowledge to reduce the house edge. But this is not what Kane did, he didn't alter his chances of winning, he altered the payout.

The real argument is not if pushing the buttons in the right order is cheating, but is it hacking? That issue seems to come down to whether or not there was an escalation of access. Did those button presses give him unauthorized access to data? He exploited a flaw to alter the payout of the game, and that is at the very least fraud. If we are using your blackjack analogy this is like he somehow Jedi mind tricked the dealer to change the payout for a 21. If I used a software exploit to get a bank computer to double my money I have no doubt that would be seen as hacking. So how is the gambling machine different?