Just because its a kids movie doesn't mean its allowed to be stupid. Sure, nitpicking Pixar is like nitpicking Disney's 'Alice in Wonderland', but with 'Cars' it just wasn't as believable. Thats what I love about Pixar - they made me think my Toys could talk. They just sold it. They made me think Monsters were nice people, they made me think Robots actually had a personality (although I still hated the ending), and they made me think my goldfish could talk. They just did it. The characters were presented in a way that made me leave my Brain back at my house. 'Cars' failed to do that. The concept that Cars have their own parallel dimension is just too far. Never have I looked at a Car and said 'My Car lives in a world where everyone is a car'.
Its a logical question as to how do Cars earn a living. What are their jobs aside from the ones at the road and at the Car Races? What else to they do aside from watch or partake in Car Racing? In every Pixar movie, the characters were an everyday object in an everyday world - apart from the Monsters, which are similar enough to humans and we see enough of their world to assume the answers to the questions presented in Cars. The Toys were Toys, and are played with. Within the movies, the issues of Toys being thrown away, sold, etc are addressed within the trilogy. The Ants are Ants and earn their living by doing what all Ants do, and are dominated by larger insects - which is what happens in real life. The other bugs we see are all real, and we assume that they do what the bugs do in real life, e.g a Mosquito would suck blood, a fly would eat crap, a slug would...be a slug etc. In Monsters Inc we see how the Monsters live enough to fill in any holes in the logic - we see that there are other jobs than scaring/laughing and that the Monsters can earn a living because their world can accommodate to them. We only see the Racing stadium and the crappy little town - no other civilised location. In Finding Nemo they are fish...they do what Fish in the real world do. In 'The Incredibles' its a tribute to the Superhero genre - so its set in the firm ground of reality. I cant be bothered to go on...you get the picture.
I dont get why everyone thinks that toys talking is the height of idiocy and illogicality. Its not. If the toys lived in a parallel dimension where everyone else is a toy that would be slightly less logical - but even a world of toys makes way more sense then a world full of Cars. My suspension of disbelief goes as far as a parallel dimension where everyone is a Monster. Anything more abstract then that and my brain taps on my shoulder.
But 'Cars' is still a good movie. Not Pixar's best, but better than most stuff out there....