#2 Google has so many popular products (search, gmail, youtube, maps) that it makes sense that they're that big. It's equivalent to a person having a bank account with $1bil in it. Just leaving that money in the account and raking interest, you just continue to get bigger by being. In google's case, there isn't strong enough competition to stop them from "being" and gaining more share based on their prior efforts.
#3 Could a new US based search engine compete with Google? Or are they just that big that the task is a fool's errand?