The article says that this sort of heavy use can be measured in oz/wk, with 1-2 oz/wk being quite a lot. I am the heaviest cannabis consumer of my peers, and I barely consume a quarter oz/wk. It sounds like addicts are much heavier users!
On the other hand, tobacco smokers can be addicts at 1-2 cigs/day, but not necessarily chain-smoking 1-2 pks/day like the most-addicted smokers. Perhaps there's a continuum.