It's not just the wages, it's the cost of health care.  America is the only 
industrialized where health care is a shared cost between the employer and 
employee.  That means, that our employers are competing with a huge chain 
around their necks that their foreign competitors don't have to carry.
Minimum wage says nothing about Health care costs.  If you get $25,000 a 
year and have to pay $200 a pay check off the top, just for health care; you 
are still below poverty.  That often includes $1,500 per person deductibles 
and co-pays for Dr. visits and prescriptions.  That is unless the specific 
drug that works for you is not on your companies drug formulary.  Then you 
pay full price for it.
Besides that, people can't afford the risk of changing jobs because they may 
have to go with out that crappie insurance, and a week in the hospital 
costing over $12,000 would bankrupt them.