The central difference may be immigrants willingness to work in particular occupations that are shunned by domestic unskilled workers. The occupations that foreign unskilled workers fall into may in some cases actually be complements to the occupations of domestic unskilled workers, and, therefore, the work of the foreign unskilled workers could raise the marginal productivity of domestic laborers, rather than reduce their wages and employment rates as the traditional model predicts.
The primary disparity involves immigrants' inclination to work in certain sectors that are not engaged in by domestic unskilled workers. The jobs undertaken by foreign unskilled workers might sometimes be supplementary to those held by domestic unskilled workers, and therefore, their labor could increase the marginal productivity of domestic workers instead of lowering wages or employment rates as traditional models indicate.