HLCbuild, in my townhouse (in Manassas) they did provide a cavity for boxes, there is the party wall which is as you described, but there are studs and another layer of drywall. They also put insulation in the wall, too, believe it or not. Incidentally, the party wall is attached to the framing of the house with metal "L" brackets which I'm told will melt in the event of a fire, preventing the party wall from being pulled down.
Apparently it works pretty well since the townhouse across the street caught fire and pretty much had to be torn all the way down. The party wall on either side was still intact.
