I suppose the difference is in Barbie's origins. She started life as a porn doll, which is hardly surprising when you look at her. And though someone said lower down (WWB?) that 4 year olds don't realise that so it doesn't matter, we can see that, and it obviously kind of does. I could give my 4 year old a vibrator to play with and she wouldn't know what it was, but I would.
Don't want to get too heavy, because my dds have Barbies and like them, but she is pretty revolting. She forms the first drop of the steady, incessant drip that leads our daughters down the path towards poor body image and ends, in the worst case scenario, in an eating disorder. Starts with Barbie at the age of 4, takes in Cat Deeley and Girls Aloud by about 7 0r 8, swings by Kate Moss and her ilk at around 14.... Which is why I always tell them that real women don't look like that!