My comment above is actually wrong. Citizenship is not a barrier to mobility of labor. People in this country are free to move about. So from a perspective of the citizen there is no such barrier and therefore from a perspective of the government there should be no need to change the immigration laws - H-1B included.
No, they are not: they are free to leave but not get jobs oversees. Americans need permits to work in the EU.
Moreover, it's not the mobility of Americans we were discussing, were we? A foreigner (non-citizen) is NOT free to come to this country (even as a tourist in the case of many countries) and work here. The lack of American citizenship is a barrier to his/her entry into our labor force.
So I think your original comment is correct.