The difference is usually a piece of paper
If the University you went to says you're a Graphic Designer, then you are. Sure, you probably have a great understanding of photography, illustration, production, even environmental and industrial design. How good of a Designer could you be without those? But, the paper says Graphic Design, and so you are.
If the University you went to gives a degree in commercial art, then they are usually making a distinction between it and Fine Art. You are usually get a C.A. degree with a SPECIALIZATION in graphic design, photography, etc.
http://dockerydesigns.50megs.com