I think what they mean is that weed won't produce any physical side effects once the addiction is not fulfilled, and there is no chemical reason why you want more; you just can't get enough of it because the effects are so awesome. I'm pretty sure I've got a psychological addiction but I don't care since I keep up on it. But in theory, you can be psychologically addicted to practically anything that gives you pleasure: that's why there are all sorts of sexaholics, workaholics, internetaholics, foodaholics...I'm a cannabaholic I guess.