Actually most American pop singer girls don't resemble each other, not like Japanese pop singers, and I don't mean because they're all pale yellow with dark hair and dove eyes. Britney/Jessica/Mandy/Christina are the closest I can think of, but they hardly resemble each other beyond being blond.

Edit: I admit I have no idea what I'm talking about when it comes to American pop, but I stand by my assertion that JPop starlets are mass-produced.