Bob, breaks like this aren't expected to stop a wildfire. They serve more as safe starting points for backfires if a fire approaching that development is imminent. In the warm, windy conditions that typically coincide with wildfires, the last thing wanted would be to start a backfire right up against and upwind of a development without a reasonable break. Aerial drops of water or retardant would also be more effective applied along the new tree line, possibly allowing any combination of the break, retardant drop and back fire to work together.
Your question about the orientation of the line is answered by looking at the path of the 2007 Warren Grove Fire. The area to the northwest of this development is less vulnerable because of several paved roads that can be backfired to protect it and the wetlands flanking the Oswego offer a degree of protection as well. The East Plains on the other hand has a long history of fire, and not just stemming from the range as in 2007.
Every development does not need to be surrounded by these breaks, but fire history usually indicates the most vulnerable ones and where the breaks are best placed.