No desert, no third world country (yet). But only ONE WiFi around: mine.
When I first installed my router, about four years ago, I was able to reach the signal from the garage. Now I'm still able to do it. I didn't measure numerically if the signal degraded along the years or not, but for practical purposes the answer is NO: I'm still able to connect from the garage, with the same two "dots" in the "intensity" display.
So, in my case, the signal did not degrade with time. Therefore, I think the neibourghs deployment theory makes sense: taking me as a "control subject" in the experiment, you can say: "The guy with no neighbours suffers no [significative] degradation in the signal intensity".