True, fantasy gambling isn't only for rogues...but aren't they the most likely to participate? Plus, I expect many gambling opportunities are sponsored by rogues.
Have you done any gambling in-game? How did your GM simulate it? What's your favorite game?
I'm a Three-Dragon-Ante fanatic, but it's pretty complicated to introduce. I imagine there are much simpler dice-based games to be playing either in the Royal Casino, or in the back of the tavern.