Just curious, what's in it for you if there are no commissions? I might use your service if you seem trustworthy.
Yes, some sort of revenue will take place in the middle-term, there might be a fee on trades, but it will always remain significantly lower than the competition.
There are other revenue sources that have to be taken in consideration when deciding whether a business model is sketchy or not. For example, an exchange service can remain free forever if it manages to keep its operating costs lower than the interests it is getting just to let its users deposits sit at a bank.
In case some of you didn't know, Bitcoin-Central.net is also a showcase for the eponym open-source exchange platform that also powers some other popular exchanges. So there is also potential revenue in expert consulting.
Oh, and if someone has concerns about security remember it's fully open sourced (the version you see on github is the version running on the server). Let me tell you that being aware of people reading your code over your shoulder is the best incentive to write secure and clean software