The only reason I could ever come up with that was plausible from a landlord point of view is in the case of escaped snakes. I've not heard of too many cases though where someone was injured or killed, just frayed nerves and one hell of a story to tell at the next company gathering. As proof a quick search on here for escaped snakes will likely turn up several threads from just the past week alone.
As for the damages thing it is comical to think about when it comes to Cats & Dogs vs snakes. We're in a apartment till our house is finished and the landlord here required a $100 pet deposit too but I wasn't worried about it. Once we moved in though I looked around paying attention to the trim boards and all the ones on corners and next to doors have been clawed to bits and painted over. Cats & Dogs are probably two of the most destructive animals yet it's easy to find so called "pet friendly" rentals but heaven forbid if you have a snake! LOL