Obviously, hosting in the US isn't a cure-all. And there are other good reasons to work with companies in Europe; for instance, their data privacy rules can often be better than ours, which can give you some commercial protections.
But these discussions about where people's email is hosted always talk about jurisdictional issues, and the only jurisdictional issue that matters here is this: if NSA is going to swipe mail from Google Mail, there's a whole fuckload of paperwork they have to do. If they want to get mail from your random email provider in Switzerland, they can just push a button.