I would say that funding and grants (or lack thereof) is one of the biggest determinants in the sciences in the US. You can choose your own PhD as long as what

I would say that funding and grants (or lack thereof) is one of the biggest determinants in the sciences in the US. You can choose your own PhD as long as what you choose is something your advisor has the money to support and agrees that it is an interesting direction to go. That's very different from choose whatever you want and more in line with what he thinks European PhD's are like.