I will admit to not reading the whole thread so forgive me if this has all been said
Firstly, microchipping is mandatory here but there is no way to enforce it. People get free to a good home kittens all the time so even if shelters, breeders and petstores kept lists they would not get full listings. We get cats in the shelter every day that are obviously owned but we can't trace their owners.
Secondly, not all pets that are not seen by a vet regularly are 'neglected'. My neighbour does not take her 7 year old cat to the vets because it stresses it out too much. It was a basketcase for months after it last went in because she 'didn't seem herself' - they took her when they believed she was sick, she is cared for just as well as mine are. But her owner does not think that the benefits of shots are worth the stress on her cat. Should she be treated like an animal abuser for that decision.
They don't even enforce animal abuse laws, what makes you think they will enforce a law that states you have to take your cat to the vet yearly?