(Yes, I know H-1Bs are supposed to be paid the "prevailing wage". Cheap foreign labor SETS the prevailing wage, and BTW, I'd be delighted to work for an H-1B's wage.)
Other important facets of the guest worker programs are that they:
1) Disincentivize the conversion of guest workers into US citizens.
2) Provide a labor pool that is more easily controlled (with respect to portability and wages) than equivalent US citizens.
The same thing applies in other countries that use similar programs - where wages aren’t so much the issue as much as the lack of freedom experienced by the guest workers.