The difference is in evolutionary class-breeding. Traditionally, in ancient times, cats were the companions of nobles and "living divines" and such, used to keep palaces and monasteries clean of vermin.
Dogs were lower class animals, used for protection by those who could not afford armed guards. Naturally, cats were thus considered even higher on the social scale than the other people working in palaces, mansions, etc. whereas dogs belonged to people who themselves had to be servile to survive, so the behavior kind of stuck with them through the generations. This can be seen in the fact that cats are among both the cleanest and laziest animals, spending the majority of their time either grooming or sleeping (despite the domestic house cat having a kill-to-eat ratio significantly higher than any other mammal. . . murderous bastards), and dogs, if not cleaned by their owners, will rot in their own filth--happily--if left to.
Also, prison guards, police and serial killers, who show a pathological need for dominance, statistically favor dogs.
That said, my favorite breed is the Chartreux; they're half way between cat and dog. Not just because they're larger than small dogs (my cat Musashi weighed 30 pounds), but because they're docile, obedient (they have a higher rate of learning tricks without reward than most cats, and the entire breed has a love of playing fetch), but still maintain enough independence that they don't seem like vapid insecure brown-nosers when they are following you from room to room.
And yes, I know people hate it when I go into sociology tangents, but it's a compulsive reflex. *Nerdily handicapped*