The Fine for Vaccinating Your Cat

I recently received the following notice from Dallas Animal Services (double emphasis in the original):

Thank you for being a responsible pet owner by vaccinating your pet against rabies. Texas State Law requires all cats and dogs over the age of 3 months to be vaccinated regularly for rabies. In order to monitor compliance with state law and to prevent the spread of rabies all City of Dallas residents are required to register their pets annually with the City. (Sec.7-4.2 of City Code). Failure to register your pet may result in late fees and/or citation.

The letter instructs me to send the city a check for $7 ($30 if the animal is "unaltered", $17 if it's been more than 45 days since the rabies shot) along with "a copy of the current rabies vaccination certificate." All this may seem reasonable, in light of the threat that rabies poses to people and other animals, but it makes little sense to me. The city knows I have a cat (three, actually) only because I took him to the vet and had him vaccinated. So in what sense is the city monitoring compliance when it tells me to send a check and a copy of the vaccination certificate? It already knows my cat is vaccinated; it says so in the first sentence of the letter. What it's actually doing is taxing people for complying with the vaccination requirement. Meanwhile, the people who aren't complying don't come to city's attention until their cat or dog bites somebody.