Well, I think the logic behind it is to sever the association between drinking/drugging and smoking since they do go hand-in-hand. Caffeine is also addictive so, apparently they are attempting to encourage cessation of
all addictions so that you can build new "reward pathways" in your brain. As I recall, it takes 90 days for the brain to really even start healing and rebuilding pathways, so that's why it is believed that if rehab is going to be effective, it needs to be a minimum of 90 days. After that, it is essential that NEW people, places and things take the place of the OLD ones so that the new reward pathways can continue to build and the old ones will continue to deteriorate. This is what the term "trigger" is all about.... if you stimulate a well-worn (but unwanted) pathway, then you run the risk of re-invigorating it and the addiction raises its ugly head again.
Great info here:
Drugs Alter the Brain's Reward Pathway
and here
HBO: Addiction: Understanding Addiction: Addiction and the Brain's Pleasure Pathway: Beyond Willpower