Your right that almost all places have incredibly outdated or just plain dumb laws, however that does not mean they can't uphold those laws. If for some reason you did hitch a horse on that street, and a police officer who for some reason remembered that law saw it, the officer could technically arrest you for it. Only way I see this happening is if you made the officer mad for some reason, but it can still happen.
I had a friend who had the same mindset you do about those old outdated laws, so he started breaking them on purpose in front of police to see what would happen. One day the police got tired of it and actually arrested him. The reason: He put his thumb on his nose and wiggled his fingers at a police officer as he walked by. There is seriously a law in New York prohibiting that. He was arrested for it and then released a few hours later looking absolutely terrified.
Moral of the story: Just because it doesn't happen often doesn't mean it can't happen. If a person breaks rules in UO all the time, one day a dev might get tired of it and decide to enforce the rule on that unlucky person.