First of all, that emotion thing goes both ways. He doesn't exhibit any sign whatsoever which could hint how good his hand is. Riker described this once as the perfect Poker-face.
Then, when Data plays Poker the very first time, he tries to play exactly like you propose and loses horribly. But Data is not a dull automaton. He learns! He can very easily compute what the chances of winning are, and has (apparently) learned during the times playing with his shipmates some good heuristics how to properly apply his information about winning chances.
Another very important point is: He is not afraid of losing. I believe this is a very important asset in Poker.
I was thinking about the "cheating" argument, and I'm not convinced. Around time 23:35 he says:
It was not my intention to deceive.
To the bellboy, when discussing how he managed to win. While deception in this context is not exactly the same as cheating, it still goes hand in hand. Since deception would help his cause just as cheating would, stating that he didn't intend to indicates that he won honestly.
How could he even survive the first couple rounds, without a big capital?
Data is quick to bet his communicator which one of the Poker players describes of family heirloom and trades for an entry capital of three Dollars. I would argue that they suspected him to have more valuables that he would be willing to sell.
Regarding this, the bellboy says:
Oh sure, they play easy at first not to scare off the marks, [..]
so it would appear they let Data win a couple rounds first, giving his internal heuristics time to adapt. With a starting capital of three dollars he probably couldn't have gone far otherwise.