http://www.cannabis.net/withdrawal/index.html
Withdrawal symptoms following cessation of heavy cannabis (marijuana) use have been reported, yet their time course and clinical importance have not been established. A 50-day outpatient study assessed 18 marijuana users during a 5-day smoking-as-usual phase followed by a 45-day abstinence phase. Parallel assessment of 12 ex-users was obtained. A withdrawal pattern was observed for aggression, anger, anxiety, decreased appetite, decreased body weight, irritability, restlessness, shakiness, sleep problems, and stomach pain. Onset typically occurred between Days 1-3, peak effects between Days 2-6, and most effects lasted 4-14 days. The magnitude and time course of these effects appeared comparable to tobacco and other withdrawal syndromes. These effects likely contribute to the development of dependence and difficulty stopping use. Criteria for cannabis withdrawal are proposed.
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One reason that cannabis withdrawal is not noted more is the fact that the chemicals are fat soluble and linger in the body for some time- so when cannabis ingestion is suddenly stopped, the cannabis built up in the body slowly decreases, greatly softening withdrawal symptoms.
Opiates are mostly water soluble and have a much shorter biological half-life. When you stop ingesting heroin, it is gone from your body much faster and the withdrawal symptoms are readily apparent.
What linger in the body are inert metabolites of cannabinoids ... so that theory falls flat.