There are actually certain states in the US that most likely have some sort of restriction on bitcoin transactions on a state level due to the fact that I see some states being singled out in the ToS of bitcoin exchanges. So it's definitely a worldwide thing.
In most cases it concerns gambling. Coinbase for example will suspend your account if you send funds to a gambling site, and they have pretty sophisticated tools to exactly know what gambling site you're sending funds to. It still happens that it catches people by surprise, but they should know that at least within the states, Coinbase is very tight with its policies.
It always has been one of the bravest exchanges in the space, so unless you're a total newbie and don't read the terms before registering, you should be aware of this.