Well sidestepping your specific loss, I think the damage done between the two species are difficult to compare - especially in their affect on humans which is where the majority of pet laws are concerned. How many house cats have mulled of a child to death? I can't think of a single park that has been overrun by cats and their feces though I know two near me that has been designated "free roaming dog parks" making them nearly unusable for human use (picnics, etc.). No one I've witnessed takes their cats into supermarkets or restaurants hoping others won't find their presence uncomfortable or unsanitary. Hell, even when visiting a home, I know more cat owners who ask or offer to lock their cat in the other room than dog owner that ever bring up that the dog could be a problem.
Again, I'm sorry for your loss, but since you brought it up in a public forum, I have to say my experience is the average dog owner is far more irresponsible than your average cat owner. Part of this is the immediate damage that can be done by the animal (though for example disposable kitty litter is recommended against for my area because of its effect on water wildlife - less immediate and similar to your case), but that's not the whole story. I know two people that have "I'm a dog owner and I vote" bumper stickers on their cars and I've never heard them discuss proposals that seemed to be in the interest also of the "non-dog owner" community. They're really pretty selfish (though others maybe need less to be because there are fewer laws). No doubt part of that is they live in small apartments where they probably shouldn't have a dog to begin with. That's a whole other part of this, but its related.
It's also related to maybe where some of our perspectives in this thread come from. Growing up in the country (where I had both as pets), there were more free roaming cats and dogs were usually running on private property, cats did cause more problems than they do now in my life (though still not remotely close to dogs where a neighbor child was killed). Now living in a city I rarely see a cat on the streets (most are inside as it's too dangerous outside - including because of dogs - who can take a cat out safely "on a leash" thus no need for the law?), and public use lands are where dogs run and crap. It's not a great scenario and we all need to compromise, but when I spread a blanket out in the park on a sunny Saturday afternoon, cat waste isn't what I'm concerned with. When I'm walking with a woman, and I'm picking up the vibe to cross the street, it's not because a large aggressive cat is walking down this side (no tiger jokes please).
Again, I'm for protecting dogs too, but as for the different number of laws between the species, I think it's quite understandable.
