Reporter from CO here. I think this is the crux of the matter. If the points about a strong underground market in the article are true, it's (IMO) due to a weakened attempt at decriminalization. Very much like bittorrents before netflix/prime were widely available with large catalogs.

Here in Sunny CO, the prop was a Constitutional Amendment, guaranteeing the right of each state citizen to grow and possess their own Marijuana, which lead to sales. -Only two cities (Colorado Springs and a mountain town IDK)- created local exemptions against retail sales. They are now suffering with badly damaged roads and limited tax revenues to fix them, compared to cities right next door that capture all the sales.

Hampered decriminalization does not rid us of the black market. The [THC] black market is _gone_ in CO because who needs it? Questionable products, limited availability, difficult logistics...no, you go to the local store and five minutes later can be higher than 5280'.

EDIT: As CP says, there were more than two cities banning sales. Actually a lot more than I knew. I'll stand by my conclusion though. The full list is here: http://webcache.googleusercontent.com/search?q=cache:11yRzRk...