@John: I agree both can win
Here is a possible explnation for those new to Forex:
Theoratically, the relationship between broker and traders is mutually beneficial as brokers usually get their profit from spread. However, there is a tendency for brokers to go against you if they dont have the capital to hedge net positions of their client. This is precisely how bucket shops started in Russia back in 90s. However, these days large brokers try not to stop-hunt as fierce competition among brokers doesnt make it a viable profitable stratagy for large brokerage firms. Furthermore, brokers also fear regulators. For popular brokers in less regulated emerging economies, mantaining good reputation is the only way to compete with brokers regulated in developed economies ie USA, UK etc. Yes, broker can cheat if they want to and the end of the day, even liquidity providers are match-makers.