This is pretty darned silly.
Most caches are found in either parks or commercial areas. Most folks to not want strangers roaming their alleys or backyards to look for caches. If you look at Belle Isle, Rouge Park, the Riverfront, Downtown, or Hines you do find lots of caches.
Detroit itself is mostly residential (though not as dense as it once was), as are the NW suburbs (Farmington, Bloomingham (yes it is made up, but you know the area), Southfield.
People do cache in the City proper and in the NW burbs, there just are few of them in these residential areas.
In addition many of the folks in Detroit aree not as well off financially as your average geocacher so there are only a few of us who live in the City proper with caches.
I have to support the person who used Grosse Pointe as an example.
