Not only does my dog act guilty when, for instance, I catch her sleeping on my pillow, but after we have had words she tries to guilt-trip me.
Dogs are more intune with peoples emotions than you would think. The tone of your voice, the look in your eyes, even the scent of when you are mad causes responses.
Dogs are the perfect companion for people. They dont care what kind of day you had, or how much money you make. They are always happy when you walk in the front door.
A better question is why they put up with us?
When my little dog has been naughty, he sits by the front door with a guilty look on his face, as though he wants to escape outside before I find the evidence.