There are 2 types of brokers in retail fx: ECN's and dealing desks: ECN's are considered "straight-thru-processing" in that the prices you see are the prices being quoted in the open market, similar to your stock quotes. Your trades are executed with people from a variety of fx brokers or even banks and hedgies. It's more complicated than that, but that's the simple explanation. This type of broker makes his money on the commission he charges you. Spread prices vary depending on the bid/ask action.
A dealing desk broker off-sets your trades with other orders on his book. Sometimes he goes out into the "interbank market" to cover a trade, but rarely. He is always taking the other side of your trades. he makes his commission on the spread between the bid and ask on the prices and these spreads tend to be constant.
These are simplistic explanations of the 2 types of brokers. Most of the horror stories you hear are about people getting hosed using these dealing desk brokers. There are a few reputable ones, including Oanda and GFT. Most are scum.
The preferred model for most traders is the ECN model as that more closely represents true market prices and is more similar to other types of assets trading. The only problem is there are a limited number of these type of brokers.
The reason why fx trading so shifty is because unlike other assets, there is no central clearing exchange that all trades go thru, like the CME or NYSE. It is basically agreements between trading partners in which the agreements can change from partner to partner.
There are many resources on the web to help steer you if you want to trade it. And yes, there are plenty of retail guys who make money trading it. There are just many, many more who lose.