Well, dogs are social animals like human beings. So they're hardwired to pay attention to social cues like a human being's happy/unhappy quotient and things like how to get into cars and open doors.

Cats are not social animals. And thus not very good at figuring out things like doors. They just don't have that much reasoning ability.

On the other hand, the cat gets along with the rabbit, whereas my dog thought the rabbit was foooood.

I will say that the rabbit is dumb, but has a little more personality than I expect from prey domesticates. Ours chases a ball, but never learned to answer to a name.