Pets get away with it because a lot of pet owners have lost their role as the leader of the house. This degradation can be seen on their tired, defeated faces when you walk in and their Labrador assumes your torso is their bed, and no amount of "Off, Drogo! Get your anus off his lips now, Drogo!" will change that. They are disheveled, subservient wrecks, catering to their pet's every fickle whim, living as second-class citizens in their own claw-marked homes.
Cats hold their own special torment for visiting friends. People don't own cats; they kidnap them and hold them against their will until an adorable form of Stockholm Syndrome sets in. They aren't easy to read as it is. They're even harder to gauge when a friend assures you they're lovable, so you reach out to pet it, only to discover otherwise after you're defibrillated back into consciousness in an ambulance. "Bad kitty," you'll mumble before you pass out again, the EMT's "Live, damn you! Live!" resounding as the last thing you hear before the loss of blood from all the scratches fades the world to black.
With some luck on your side, a person's cat will flee at the first inkling of another human's arrival. And that can sometimes be a best-case scenario with a cat -- that it runs away in terror, never to be seen or heard from again. The worst-case scenario is that it sits, like a troll in a folk tale, waiting for you to get cocky enough to try to pet it. Waiting for you to become stupid enough to embrace death.
In the same vein, upon entering a house with a cat, an owner might say, "And we have a cat. He's ... here, somewhere," speaking of the presence of their own pet the way people talk about the lingering spirit of a deceased relative. The cat might be here; you just have to believe. It's a gorgeous cat, they assure you. Very friendly, loves getting its head rubbed. Now if only we could gather enough people for a proper seance to summon it.
Or just shake it's bag of food and watch it drift around corners and leap tall buildings in a single bound.
Other people's dogs present the opposite problem -- they're too present. You can feel their overbearing love before you walk in the door. All guests who visit my home have to physically brace themselves for impact, because when I open the front door, a dog torpedo will launch into their chest. My dog runs so fast from the far end of the apartment to the front door that if I screw up the timing, she's going to Kool-Aid-Man through that door. I can see how that can be annoying to guests, but hearing friends and family grunt from the impact just as they start saying "Hello" will never stop being funny.