I'm linking to this post not because I'm in favor of more casino games on iOS, but because I want to highlight just one way your app can get in legal trouble. Some states would like to consider certain types of apps as gambling apps. This post helps you steer clear of this kind of legal issue in your app. You may surprised at the types of apps being targeted.
Two other examples I see a lot are the use of copyright images and trademarks. If you are using a trademarked name in your app name or description, you run the risk of legal ramifications. Same goes for celebrity images. These are not images you can use for free in your app. You are profiting by using that celebrities image without compensating them. That is against the law. If your app has any degree of success, you can expect a notification from the copyright holder through Apple.
How to Design Mobile Games to Avoid Anti Gambling Statutes by David Almeida and Mark Eisen from App Developer Magazine