The cleaning of the plate should not be the issue but the fact that this is allowed to happen. Dog, cat lover or not there is a perception for most people that having animals in and around where food is prepared and eaten in a public environment is unhygienic, which is what started this thread.
I totally agree with nicola's comments where visitors to a resturant feed the cats/dogs and then leave an animal who will now becaome a nuicence to others. For the majority if you see this kind of behaivour you would not visit/return to this establishment no different to if you saw somewhere that had a bad fly problem and did nothing to resolve it is most likely that you would avoid.
Mind you I have seen some people who should not be allowed in resturants and not just because of the areas that they can lick