"slave wages" is not exactly correct. If a chinese worker from the south of china goes to north china to work for a couple years making shower curtains, they return home and pay cash for a house.
What you consider slave wages is a lot of money to them. If you went there and did the work, you'd consider it slave wages, but they consider it very good money.
Their cost of living is significantly less in most of China than the Western costs of living. However Beijing is getting fairly pricey rents now, approximately $400 per month and it isn't uncommon to see them in the 1000's. I'd hardly say the chinese workers are paid slave wages when apartments near me are listed at $600.
What you consider slave wages is a lot of money to them. If you went there and did the work, you'd consider it slave wages, but they consider it very good money.