He's definitely talking down to his audience, but this has been a long time coming. Any ex-witness who left more than a decade ago can see that the new literature has been dumbed down to keep pace with the average witless's declining IQ: sentences and in fact entire articles are shorter than they once were while precision and clarity in word choice have been sacrificed so that even readers with a very narrow vocabulary can understand.
I don't think Lett is retarded, he's just smart enough to know that most of his audience is.