Yeah, that's what I get for posting in a hurry! You definitely get some yeast reproduction in the wort, but the yeast should be built up and ready to go before it's pitched. In other words, you don't want the entire reproductive phase to take place in the wort. It's especially important in the case of liquid yeasts which need to be roused out of a deep sleep (I don't know the proper term). Not only is it not ready for fermentation, it's not ready yet to reproduce. So you don't want to just pitch a vial or smack pack and hit it with oxygen.
As far as over-aeration, I really don't know the how or why. I'm just repeating what I'm reading about it. Check out the link from my previous post.
Funny. We were both saying the same thing. But in different ways.