Copyright is automatic in all countries that have ratified the Berne Convention. Countries that have ratified TRIPS (which is a requirement for membership in the WTO) also follow the Berne Convention rules. There's a handful of countries that aren't members of the WTO that don't follow these rules. I would assume that enforcing copyright in these countries might prove problematic with or without a copyright notice.
How much of Berne is included TRIPS is interesting and rather telling. Yes, automatic copyright is included. Where it gets interesting is when you review how they made sure there are no loopholes towards intellectual property rights while explicitly excluding moral rights...
