There's police in Manehatten, a sheriff in Appleoosa, and I really don't think they were really focusing on law enforcement. The fact is, they have a military force specifically so they can guard the princess, proving not everything is sunshine and gumdrops in Equestria. We don't need to wait for a police episode to make the logical leap that in every large gathering of ponies, there is at least ONE pony who's purpose is upholding the law. HOWEVER, that doesn't mean there are any laws to uphold. It's more likely that these ponies are simply peacekeepers rather than law enforcement. Cabelleron may not have broken any laws because there are no laws that he can even break. I haven't put a lot of thought or research into it, but it doesn't sound weird, looking at how Our Savior the Godprincess Celestia deals with Twilight and her friends, or the kind of people she has punished. It's possible that Celestia may not have created any actual legislature for Equestria, and only punishes those who threaten the very nature of Equestria itself until they have a chance of reforming. That's why Starlight Glimmer wasn't really punished FOR BREAKING TIME, or Twilight was only scolded for messing with the minds of Ponyville's entire populace. They didn't break any laws, they just disappointed Our Savior the Godprincess. Celestia IS Equestria's mother. Like, that is pretty much indisputable at this point. Equestria loves Celestia, and Celestia loves Equestria and wishes to guide it in an appropriate direction. I know not everyone can relate to this, but I love my mother. I don't want to disappoint her because I love her. I like to think that Equestria feels the same way to their mother, which is why bad doing doesn't happen on any large scale. Can't call it crime since there'd be no laws.
Uh, I didn't really put that much thought or research into any of this, it's just a theory I had. I don't know how much standing the theory has, but it's an interesting thought. At least, i think so.