Please Explain This Anomaly

Is…is this a job for human rights activists or for PETA?
Okay, this is something that has bothered me for years, and in all sorts of medium.
So I'm furnishing my little Animal Crossing cottage, right? But I don't know if I'm comfortable with keeping a caged canary (which is a furniture item) in the window when my next-door neighbor is a talking, four-foot-tall robin.
It's the same thing in what was one of my favorite children's show, Arthur, too. He's got a little pet dog, but one of his best friends is also a dog. And it happens again with Goofy and Pluto of the Disney universe; both are dogs, but they live in different castes of domestic hierarchy. What is this?
And when you encounter this sort of thing at such a young age, it's… I don't know, it's just crippling.