Or, the more likely theory: one of the animators was bored and thought it would be neato to give the pizza truck a cameo appearance. Of course, he pointed it ou

Or, the more likely theory: one of the animators was bored and thought it would be neato to give the pizza truck a cameo appearance. Of course, he pointed it out to a few of his close friends and a free of the people he worked with. As Pixar continued making movies, someone would always sneak the pizza truck in, to the point it's become an integral point in their corporate culture. A Pixar movie wouldn't feel the same without looking for that cameo appearance - for the employees just as much as the consumer. So yeah, you're right. They do all take place in a unified universe: ours. Where people are people and they do silly, fun things for the sake of them being silly and fun. Like discussing unified universe theories of movies as if there's been any shroud of evidence that would lead anyone to believe one should exist.