In my line of work, I've seen people addicted to just about anything. However, my definition of addiction is different than the 'lay public' (i.e. non health care professionals)
Physical Dependence is when the body 'has to have the drug' in order to funtion normally. The classic example is the herion addict. As long as he gets his dose of smack, he functions normally, liek anyone on the street. When he doesn't he experiences true withdrawal symptoms.
There can also be psychological dependence, where the patient's MIND tells them they have to have it. The old classic example here is the Valium poppers of the 1970's. They think they cannot cope without 'taking a pill" and take more and more.
Addiction is the seeking of the drug beyond normal medical treatment. Addiction itself is crimiinal, drug seeking behavior. So, the alcoholic that goes to the liquor store every night is showing dependence. When he steals the alcholo because he is now unemployed and has no money, he is showing addictive behavior.
So, yes, I've seen "addiction" to pot. I've even seen a patient addicted to over the counter stuff like Benadryl. It doesn't even have to be a drug. Look at all the men (and sometimes women) that are addicted to pornography. Even some of those who do the massively extreme sports are considered to be addicted to the high from the adrenaline and endorphins (the natural form of morphine your body creates for pain and euphoria_. The human mind can be a great thing, but also a very obsessive and compulsive one as well...