said by Hydroshock:That's not just a function of US law - it's the fundamental principle by which copyright works. Essentially, anything you create belongs to you and others can't just steal it or misrepresent it as theirs. Copyright is however a relatively weak instrument since it only applies to tangible creations and not ideas or concepts (which is where patents come in).
Well they can slap "copyrighted" on anything these days. The way the U.S. Copyright laws work, everything is copyrighted the moment it is written and doesn't need to be filed or anything. (including things as simple as emails). Problem is proving it was yours first without filing it.