White collars have always had better salary growth than others. Generally, blue-collars rely largely on 'manual labor' and, therefore, after its peak productiv

White collars have always had better salary growth than others. Generally, blue-collars rely largely on 'manual labor' and, therefore, after its peak productivity, they hit a depreciative tendency(younger employees/outsourcing/...) . White collars rely largely on networking and influence, hence its 'productivity' continues to grow. The more 'manual work' one performs, the smaller his salary growth is.