There are several reasons why apps are published/released region specific. One of the most obvious reasons is legal issues. What is allowed in your country might possibly be not permitted in mine and vice versa.
Another very obvious reason is that an app may offer a service which isn't broadly available. Take Netflix for example. Their service is not yet available in Germany, hence it doesn't make much sense to offer their WP app in our store.
Regarding Creative Studio I agree though. I don't see any reason to not offer it world wide.