probably because the new worker is required to have social security, payroll taxes, workmans comp....paid by the employer (and if they pay that employee under the table they are doing so illegaly so the argument is moot) which drives up their per pound price.
for me, i would just like to benefit from the produce that is grown localy to my home. we are surrounded by fields of fruits, veggies and nut products yet we never see them in local groceries, all are shipped out across the country or overseas. we instead get "hot house" imported products which are greatly lacking in quality.
and while i can't speak to other parts of the country, our produce prices have quadrupled in the past year, and we have yet to see a real impact from fuel cost increases. i personaly would welcome the opportunity to shop at a
walmart for food items, but californian communities have taken to fighting against their building-in large part because a lot of people feel they do not offer a "living wage" to their employees.
You've presented one scenerio "Demand is constant". The great thing about Economics, there is always another "what if scenerio", another theory to counter the one you've just presented 
Yep, on the short run curves, as an employer, I'll suck up the higher priced domestic wages, but in the long run, there's this great global economy waiting for me. Can you say outsourcing?
