Not having time to dissect this statistic, I'll point one "little" thing that gets always omitted. Lets say the bottom 50% is not progressing much or at all and this graph is true. It means they can buy exactly same amount of things in 60s and 2010s, to justify stagnation of wages when inflation is taken under consideration. Now, we have to realise that things frm 60s are not exactly same things as now. Take a car for example. Today's cars contain standard features like power steering, air conditioning, airbags, stereo, safety features, 3x more efficient engines, intermittent wipers, cruise control, lots and lots more technology which didn't exist in 60s or was optional and only standard in cars for rich. Let's look at houses. Today's houses are twice bigger with superior windows and insulation, few times more wiring and electrical fixtures, and contain appliances which didn't even exist in 60s. Look at telephones, they were only black, stationary with expensive service. Today they are portable, smart and with application for everything. Food is more delicious, with variety, and contains more calories (reasons why people are fatter these days), movies - you don't even need to leave your house, vacation - for 1000 bucks all inclusive in Mexico with a flight included (unheard of in 60s), etc, etc
So even though this statistic shows stagnation for bottom 50% there was a tremendous progress in their standard of living too.