And it has more to do with urban vs rural or suburban than it does with anything else. Suburban slackers sitting around in the mom's basement are simply less likely to get caught with pot than urban smoking in the park or walking around on the street carrying it and committing other crimes.

How different communities are policed to have an affect as well. Clean and well kept communities to have "broken window" policing so police are more likely to look for things like pot.

For the record I do believe black males are policed more heavily than white males but I think the thug culture plays a big of role in that as racism does and as long as it is embraced or at least tolerated but large numbers in the black community nothing will change.