Should you suddenly feel compelled to study the economic arguments that might justify why the very rich are so very rich and why the rest of us are not,
you can read Mankiw's paper (pdf).
My impression, after reading it, is that Mankiw tries to explain increasing income inequality in a world where tax policies have never changed in the direction of benefiting the wealthier, where outsourcing and globalization are not fairly recent phenomena, and where all markets are not only very competitive but where we all can immediately spot the true marginal productivity of all financial firm managers!
For more erudite criticisms, go
here,
here, and
here. More on the topic
here and
here.