I don't talk to my dog except in baby talk! Or most other animals for that matter. Yes, I'll admit that when I meet a new dog or cat, I'll immediately start cooing to them—"Who's a handsome boy? You are! Yes you are!"—even in front of other people. I've never had anyone say anything, however, and most people just join in
I think it's very, very common in the US and northern Mexico (where I live) for people to talk to their animals in silly voices. The few times I've seen people talk to their animals in a normal tone of voice, it meant the animal did something wrong.
I was out all day today with my chihuahua and had a handful of people come up to him throughout the day and talk to him—every one of them in a high-pitched voice. Reminds me of this xkcd comic about cats.