When we say that a thing which does not create changes in our physiology that produce pain, sickness, and even death upon sudden withdrawal, we are speaking metaphorically-- i.e. we are saying that the desire to do X is so intense that it feels physical.
With pot (as with cocaine, sugar, fat, masturbation, etc) the question of physical addiction is not the correct one. The question is why some people find pot and any of these other things-- things that don't produce acute physical pain and discomfort upon withdrawal-- preferable to a reality without them. And the answer always has more to do with that objective reality than with the character, or whatever, of the individual him/herself. Why is contemporary life so empty for so many of us that even a few mins of easy pleasure is endlessly, repeatedly, preferable to experiencing it unmediated? As someone prominent in the movies business once said to me about cocaine, it only becomes a serious problem for you if it's the best thing in your life. And, apparently, even for some very famous and successful actors, it was!