I think cat-owners need to be more responsible about their cats. I live in a suburban community, where many people allow their cats to freely roam. So the cats poop in my garden, dig up newly planted flowers, scratch up my car, and try to "fight" with my cat through the patio doors (and then he gets all upset and territorial and starts peeing on things). These are well-fed cats wearing collars, so I know they belong to someone. If I can control my cat and keep him inside, why can't other pet owners? I think leash laws should be applied to cats just as they are to dogs.
As to the OP -- I have to agree with several other people in this thread. The owner of the cat bears some responsibility, since the cat was outside, unleashed. The dog owners should help some towards the cost, though.