Actually, the best part of that page is drug fact 201.  That statement is clarified with more detail in the following:

 Brick, J. and Erickson, C.K., Drugs, The Brain, and Behavior: The Pharmacology of Abuse
and Dependence. Haworth Press, Binghamton, NY (1999).

Then check your definitions of Addiction and Dependence here:

 Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision
(DSM-IV-TR), American Psychiatric Association, Washington, D.C. (2000).

and one last really light one to tie the whole thing together:

Wagner, F.A. and Anthony, J.C., From first drug use to drug dependence: Developmental periods of risk for dependence upon marijuana, cocaine, and alcohol. Neuropsychopharm.
26: 479-488 (2002).

And now...it's Miller Time.  For those non-americans...have a Watneys.

PRH