Occasional Links & Commentary discusses how higher productivity doesn’t necessarily translate into higher wages.
For example, in terms of numbers: if real wages increase by 10 percent (workers are buying more things) but the prices of the items in the wage bundle (food, clothing, shelter) decrease by 20 percent, then the value of labor power (what capitalists have to pay to get access to the commodity labor power) will decrease by 10 percent. Voilà! Higher real wages can be (and, throughout much of the history of U.S. capitalism, have been) accompanied by rising exploitation.
And that’s precisely one of the effects of increasing productivity: it lowers the exchange-value per unit use-value of wage commodities. Less labor is embodied in each unit of bread, shirts, and housing. The fact that workers are able to purchase more of those commodities (say, at the same rate as productivity is increasing) doesn’t mean exploitation is not also increasing.