I wondered about this when I went into treatment for alcoholism. I was an occasional smoker (about once every couple of weeks and then only with one or two particular friends) for years and years.
I never had any troubles with pot, and, in fact, I share the experience of finding that smoking it actually reduced my desire to drink. (However, for that to be an effective tool I would've had to smoke all the time, which didn't appeal to me.)
The few times I actually managed to get my hands on my own supply, I usually found myself eventually throwing a bunch of it away because it would dry up and go bad. That's how seldom I actually used the stuff, even when I was fully stocked.
All that said, I have come to the realization that, since getting sober and beginning to work the steps, I no longer have any desire for acute chemical mood enhancement. I could probably rationalize using it because it wouldn't cause me harm (though it probably would), but the fact is I just don't want to.:atv