Your post got me laughing out loud – what a charming perplexity. I've never been at all fond of Barbie, either. Stepford, uh, Bunnies! I love it!
I watch the way my imaginative grandboy, going on 3, interacts with his toys, and it doesn't seem important to him what sort of details they do or don't have. They are simply props for some playful storyline he concocts, and those storylines are evolving quickly at his age. His imagination supplies the details needed for his games, just as it would if he were playing with a big empty box.
I sincerely doubt that your son is learning those things about women's bodies that you are worried about. He's got your figure as his prime example of what women look like, right? And female relatives, and ladies in the grocery store, and ….
I believe in teachable moments, and these often occur in response to some form of cognitive dissonance: a model or concept suddenly doesn't make much sense when compared to actual experience. At some point, maybe at 4, or 7, or whenever (if he hasn't thrown Barbie over for more "manly" toys like cars, rockets, or guns by then), he may actually comment on Barbie's amazing proportions.
At that point, I hope you'll share with him your feelings about the objectification of women. And, at some point, your feelings about the objectification of of men (breadwinners, soldiers, spider-killers, whatever you've noticed). And of children, or money, or factory-raised chickens, or whatever else is of concern to you.
But to be more realistic, who could possibly say all that? Who could possibly take in all those words? No matter: example makes a deeper and durable impression. So really, the best we can do is to honestly live what we understand. THAT is what our children actually learn from us.
In the meantime, I'm guessing the Barbies will probably be thrown over for some other favorite toy before long. Smile, mommie!