My experience is that working conditions are very related to quality. For example, a messy factory is both hazardous and a sign of lack of discipline.
Labor in China is quickly rising in cost, and poor working conditions are being punished in the marketplace. It is not always easy to get more labor, and when you can get it, it's more demanding (shorter work hours, nicer atmosphere, less stressful, etc).
So while reasonable working conditions are a must from an ethical perspective, they are also necessary for purely business reasons.
And working conditions, please. People everywhere deserve to be reasonably paid and have safe working conditions.