If you write or create something you own the copyright automatically.
Publishing is not writing. If I take an article from a printed magazine or book and publish it online I have published it first online, but I am not the writer and not the copyright owner.
Many people complain that Google could simply identify copyright infringment by checking who put a text online first. However being the first online publisher is not an indication of holding the copyright. You could have ripped the text from an offline source or from a "subscription only" website where search engines have no access.
So search engines have in fact no clear indication who is allowed to publish a certain text and who not. They can make educated guesses but that's all. Which means webmasters and content writers have to take care of this problem themselves.