Good point. Instead of calling the game poker it should be dressed in Wall St jargon, and it'd be legitimate investing. The players can be called brokers, the cards are securities, a hand would be called a compound derivative, the ante is an investment, and the pot is just a leveraged mutual fund. The only problem is good poker players get a higher return than good brokers do.
I agree with you in principal but there is one difference...
Gambling involves the creation of risk to speculate on for no other reason than the thrill of speculation.
Participants in financial markets (at least in theory) take positions in risk that already exists. In other words, they assume existing risk for others.