So, although workers of today are more productive - per dollar paid per hour/month/year, is it possible that people haven't actually been working harder but rather machines have been doing more work? Is it possible that these productivity gains represent value provided by giving every office an IT department rather than people working better (or harder or smarter)?
I think it is possible, but I don't think it is a satisfactory explanation. It could simply be the effects of supply and demand on the marketplace. Beyond a certain point, money doesn't buy happiness so I see no reason why the upper end of salaries would increase other than pure greed (which is consistent with lots and lots of increases in executive pay) and unskilled labour provides minimal value so why would machines making one interchangeable labourer able to do the work of two or three interchangeable labourers lead to an increase in the pay of interchangeable labourers?