The following quote is the best statement I've seen about the question of whether or not sex can be an addiction.
"Addiction is a physiological dependence. When alcoholics stop drinking, they get the sweats, their heart rates goes up, their reflexes increase, etc. They can even develop the DTs. Heroin addicts have their own withdrawal syndrome, but again it involves physiological changes (I do not mean to imply that there are not psychological changes as well.). If sex "addicts" are denied sex, they may have all sorts of psychological problems, but they do not go into a physiological withdrawal. For your information, addiction is not listed in the DSM-IV; it is called dependence."
Charles Moser, M.D., Ph.D.