The most obvious thing: customers are only allowed to take one side of a bet, whose terms are dictated by the house.

But no casino has a monopoly on roulette. Yet the market doesn't seem to drive the odds to their correct values. Dagon notes above that regulations make it hard to enter the market as a casino. Maybe that explains why my naive expectations don't happen.

Actually this raises another question for me. If I start a casino in Vegas, am I required to sell roulette bets as though the odds were p = 1/36, instead of, say, p = 1/37 ?

[Edited for lack of clarity.]