Most countries are sensible and allow people to stay airside without passing immigration and customs controls, but not the US!
Not true. Depends on whether the flight is a through flight or a via flight on the flight plan. Many airports use a separate gateway for those passengers as the only reason the airplane landed in those cases is a tech-stop, extra fuel due to strong winds, etc. etc. We treat our passengers exactly the same way we get treated in other places, whether in Narita, Singapore, Shanghai, or Cologne. Border control needs to be strenghtened and therefore I like the idea everyone uses a passport today. Those "new" 24/7 updating rules helped us catch this dirtbag:
washingtontimes.com/news/2010/may/04/new-york-car-bomb-called-act-of-terror/