Well that is how exchanges live and survive and earn money. But not all exchanges have a high success rate. Exchanges spend huge of amount promoting their website and have paid a number of people to be known and to gather more clients. Without clients exchange will bound to fail. I remember the exchange live.megacrypton, it disappeared from the web since only a few users are trading.
Aside from the huge income, the exchanges also make sure that all coins in their site is moving and so they create transaction flows which sometimes are risky and cause them to loss a significant amount of btc.
The exchanges are making a huge amount of profit without a doubt and since it is a global platform without any limitations, the opportunity is huge and many are taking advantage of it and i do not think that the exchanges will create fake volumes to keep the flow moving and if anyone does those things, they are just inviting trouble, if you start faking things, you will never succeed with your project.