More or Less?

This is taken from Myths of Rich & Poor by Michael Cox and Richard Alm. Real wages, as we've heard, have been going down. (In constant numbers, yadda, yadda, yadda.) However (as the chart shows,) the cost of food (in labor) has gone down even as the price has gone up. [The chart is for the USA.]

This asks some interesting questions: Are real wages going down because so much other stuff has been added to the CPI? (consumer price index) When budget proportions change, (I'm thinking of housing vs. food,) does it make an apples-to-apples comparison still possible. How much of purchasing power is affected by the bidding-up phenomenon Elizabeth Warren points out in The Two Income Trap? Does it make the numbers more unreliable? And what, for that matter, does Robert Reich think of all of this?