I'm not sure of the reasoning behind the number of dogs one can own, but I have a good idea... My parents are 75 yrs old. My Dad spent many years prettying up their back yard so my Mom would have a nice place to sit in the evening (she has been ill for a long time). People moved in behind them with 7 or 8 dogs, every time she would go out her back door these dogs would attack the fence and bark non stop at her. So she just stopped going outside.
Someone else in the neighborhood must have reported them because the dogs are no longer there. On the licensing note, I did notice at the bottom of my water bill last month there was a phone number to register your dog with the city.