Well that's the flipside of the argument. The point isn't that kids identify with white people because people are inherently more identifiable - the point is we put white people all over the bloody place to the point that people strongly connect white == good guys. That experiment is one of the reasons that I'm upset with hollywood in general, and Avatar was the first film where I finally got pissed enough to complain to the producers about it. (In the grand scheme of things I honestly don't think it's the worst of sins for Avatar to have an all white cast, but it was the last straw for me).
The kids in avatar aren't "easily identified" because they look white IMO, it's just that they have a style that we normally associate with blank slate, and people have come to associate "blank slate" with white. (There's an article out there somewhere about how most black superheroes are either the black version of a pre-existing superhero, or instead of a normal costume they just have an outfit that particularly emphasizes "blackness.")
What I actually wish is for hollywood to make more movies and TV shows with protagonists that aren't white, without having any particular "ethnic" vibe to the role. (Hollywood has demonstrated a tendency to underestimate people's willingness to enjoy films than run against the current demographic bent, for example they tried to kill the Kirk/Uhura kiss in Star Trek, but when it went on the air as originally planned they got tons of fan mail. They also originally didn't think even Will Smith could play the lead in Hitch, because it was "common knowledge" that people didn't want a romantic comedy starring a black guy).
I can't really complain about any particular movie that has no racial bent that happens to star white people (well, I guess I could, but it would feel silly). But when you take a movie about an asian world and turn the protagonists white, I feel justified in bitching.