I don't quite see your definition. A zero sum game is between two, and casinos are far from that. Not even a poker table with only two players would be a zero sum game because the house collects rake, as you pointed out, so we have a third player in play. And if we take other games that are not games of skill, such as roulette, neither, because there are several players playing against the house. I think the closest thing would be a game where you play alone against the house. But in any case the analogy doesn't seem to me to be the most appropriate.