With children, it's expected, because many of them act that way over other things, as well. It's not unusual to see a kid tell another kid that their toy is "stupid" when anyone can see they're fighting their own jealousy over it. Jealousy with children often results in anger, denial, and bad rationalizations. It's when people don't grow out of this as they get older that things turn ugly.
Still, it's not like this is true of everyone. As someone who ran a video rental store for years, I've seen a lot of what you're talking about, but I've also seen a lot of kids react dead opposite and say, "man, I wish I had a PS3/Xbox/Wii". It's kind of funny, because a lot of times they would just stand there, staring at the box art, playing the game in their head. I'm not just talking about a few seconds, but several minutes at a time. You'd even see the same kids come back another day and pick up the same game case again and stare at it.
Kids are also filled with misinformation from friends. Some of it will make you facepalm. That's when I smile, pat them on the head, and tell them why Playstation is better.