Is there a difference in automobile oil and motorcycle oil?

According to the motorcycle dealers, yes. The additives are different. A test done by by John C. Woolum/ Ph.D.

Professor of Physics

California State University, Los Angeles shows that the testing of motorcycle oil against automotive oil shows no difference in favor of motorcycle oil. In fact the lowest score in viscosity were the motorcycle oils themselves. All of which were out performed by SG rated automotive oils. Source : http://www.nightrider.com/biketech/oiltest1.htm