Call me a cynic, but "human being" would probably get replaced by "citizen" in the real world anyway. 
First Law: "A robot may not injure a U.S. citizen or, through inaction, allow a U.S. citizen to come to harm."
-> Allows the construction and deployment of military robots for combat purposes. You may wan't to have robots who are allowed to kill citizens of foreign countries.
Second Law: "A robot must obey orders given to it by U.S. citizens, except where such orders would conflict with the First Law."
-> See above. It also means that an illegal immigrant wouldn't be authorized to order a robot to do things.

First Law: "A robot may not injure a U.S. citizen or, through inaction, allow a U.S. citizen to come to harm."
-> Allows the construction and deployment of military robots for combat purposes. You may wan't to have robots who are allowed to kill citizens of foreign countries.
Second Law: "A robot must obey orders given to it by U.S. citizens, except where such orders would conflict with the First Law."
-> See above. It also means that an illegal immigrant wouldn't be authorized to order a robot to do things.